Allow files creation in /tmp on OpenBSD (#3512)

- src/protector/protector_openbsd.go: add tmppath for pledge
    permissions
  - fix #3511

Signed-off-by: Laurent Cheylus <foxy@free.fr>

src/protector/protector_openbsd.go

@@ -6,5 +6,5 @@ import "golang.org/x/sys/unix"
 
 // Protect calls OS specific protections like pledge on OpenBSD
 func Protect() {
-	unix.PledgePromises("stdio rpath tty proc exec inet")
+	unix.PledgePromises("stdio rpath tty proc exec inet tmppath")
 }