Standardise and add safety comments.

These will soon be required by a lint.

Bug: 290018030
Test: m rust
Change-Id: If62281a5eb2160061a11f28588b7a14e32ce265b
diff --git a/vmbase/example/tests/test.rs b/vmbase/example/tests/test.rs
index 3594523..2b6dfbc 100644
--- a/vmbase/example/tests/test.rs
+++ b/vmbase/example/tests/test.rs
@@ -143,6 +143,7 @@
 
     // SAFETY: These are new FDs with no previous owner.
     let reader = unsafe { File::from_raw_fd(reader_fd) };
+    // SAFETY: These are new FDs with no previous owner.
     let writer = unsafe { File::from_raw_fd(writer_fd) };
 
     Ok((reader, writer))