Fix clippy::precedence warning

```
error: operator precedence can trip the unwary
   --> tests/auxiliary/mod.rs:178:38
    |
178 |   const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64) << 56
    |  ______________________________________^
179 | |     | ('l' as u64) << 48
180 | |     | ('p' as u64) << 40
181 | |     | ('r' as u64) << 32
182 | |     | ('o' as u64) << 24
183 | |     | ('f' as u64) << 16
184 | |     | ('r' as u64) << 8
    | |_______________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence
    = note: `-D clippy::precedence` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::precedence)]`
help: consider parenthesizing your expression
    |
178 ~ const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64) << 56
179 +     | ('l' as u64) << 48
180 +     | ('p' as u64) << 40
181 +     | ('r' as u64) << 32
182 +     | ('o' as u64) << 24
183 +     | ('f' as u64) << 16 | (('r' as u64) << 8)
    |

error: operator precedence can trip the unwary
   --> tests/auxiliary/mod.rs:178:38
    |
178 |   const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64) << 56
    |  ______________________________________^
179 | |     | ('l' as u64) << 48
180 | |     | ('p' as u64) << 40
181 | |     | ('r' as u64) << 32
182 | |     | ('o' as u64) << 24
183 | |     | ('f' as u64) << 16
    | |________________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence
help: consider parenthesizing your expression
    |
178 ~ const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64) << 56
179 +     | ('l' as u64) << 48
180 +     | ('p' as u64) << 40
181 +     | ('r' as u64) << 32
182 +     | ('o' as u64) << 24 | (('f' as u64) << 16)
    |

error: operator precedence can trip the unwary
   --> tests/auxiliary/mod.rs:178:38
    |
178 |   const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64) << 56
    |  ______________________________________^
179 | |     | ('l' as u64) << 48
180 | |     | ('p' as u64) << 40
181 | |     | ('r' as u64) << 32
182 | |     | ('o' as u64) << 24
    | |________________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence
help: consider parenthesizing your expression
    |
178 ~ const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64) << 56
179 +     | ('l' as u64) << 48
180 +     | ('p' as u64) << 40
181 +     | ('r' as u64) << 32 | (('o' as u64) << 24)
    |

error: operator precedence can trip the unwary
   --> tests/auxiliary/mod.rs:178:38
    |
178 |   const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64) << 56
    |  ______________________________________^
179 | |     | ('l' as u64) << 48
180 | |     | ('p' as u64) << 40
181 | |     | ('r' as u64) << 32
    | |________________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence
help: consider parenthesizing your expression
    |
178 ~ const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64) << 56
179 +     | ('l' as u64) << 48
180 +     | ('p' as u64) << 40 | (('r' as u64) << 32)
    |

error: operator precedence can trip the unwary
   --> tests/auxiliary/mod.rs:178:38
    |
178 |   const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64) << 56
    |  ______________________________________^
179 | |     | ('l' as u64) << 48
180 | |     | ('p' as u64) << 40
    | |________________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence
help: consider parenthesizing your expression
    |
178 ~ const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64) << 56
179 +     | ('l' as u64) << 48 | (('p' as u64) << 40)
    |

error: operator precedence can trip the unwary
   --> tests/auxiliary/mod.rs:178:38
    |
178 |   const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64) << 56
    |  ______________________________________^
179 | |     | ('l' as u64) << 48
    | |________________________^ help: consider parenthesizing your expression: `((255_u64) << 56) | (('l' as u64) << 48)`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence
```

tests/auxiliary/mod.rs

@@ -175,14 +175,14 @@ pub(crate) fn perturb_one_header(workspace_root: &Path) -> Option<PathBuf> {
     path
 }
 
-const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64) << 56
-    | ('l' as u64) << 48
-    | ('p' as u64) << 40
-    | ('r' as u64) << 32
-    | ('o' as u64) << 24
-    | ('f' as u64) << 16
-    | ('r' as u64) << 8
-    | (129_u64);
+const INSTR_PROF_RAW_MAGIC_64: u64 = (255_u64 << 56)
+    | (('l' as u64) << 48)
+    | (('p' as u64) << 40)
+    | (('r' as u64) << 32)
+    | (('o' as u64) << 24)
+    | (('f' as u64) << 16)
+    | (('r' as u64) << 8)
+    | 129_u64;
 
 fn perturb_header(path: &Path) {
     let mut file = fs::OpenOptions::new().read(true).write(true).open(path).unwrap();