Fix path usage on windows

The pytest subunit plugin was loading test paths incorrectly on windows
as a posix path. This was causing the test loading to fail unexpectedly
because pytest was unable to process the posix path version of a windows
path. This commit fixes this issue in the pytest plugin.

stestr/pytest_subunit.py

@@ -29,13 +29,13 @@
 from subunit import StreamResultToBytes
 
 
-def to_path(testid: str) -> pathlib.PosixPath:
+def to_path(testid: str) -> pathlib.Path:
     delim = "::"
     if delim in testid:
         path = testid.split(delim)[0]
     else:
         path = testid
-    return pathlib.PosixPath(path).resolve()
+    return pathlib.Path(path).resolve()
 
 
 # hook