Add a "SAFETY:" comment in PlatformBitness::current()

The `GetCurrentProcess` and `IsWow64Process` Windows API calls
(mediated through the `windows` crate) are pretty straightforward,
and this code is only in the test suite, not in production. Still,
it's probably best to have a "SAFETY:" comment where `unsafe` code
is used. This adds such a comment, covering those two calls.

Author: EliahKagan

gix-path/src/env/git/tests.rs

@@ -181,7 +181,11 @@ mod locations {
             // is for the test suite, and doing it this way allows problems to be caught earlier if
             // a change made on a 64-bit development machine breaks the IsWow64Process() call.
             let mut wow64process = BOOL::default();
-            unsafe { IsWow64Process(GetCurrentProcess(), &mut wow64process)? };
+            unsafe {
+                // SAFETY: `GetCurrentProcess` always succeeds, and the handle it returns is a
+                // valid process handle to pass to `IsWow64Process`.
+                IsWow64Process(GetCurrentProcess(), &mut wow64process)?;
+            }
 
             let platform_bitness = if wow64process.as_bool() {
                 Self::Is32on64