Add reveal_type to test to verify commit stays str | None

Author: calm329

test-data/unit/check-unreachable-code.test

@@ -1655,5 +1655,5 @@ main:4: error: Statement is unreachable
 # flags: --warn-unreachable
 from typing import Any, Optional
 def main(contents: Any, commit: Optional[str]) -> None:
-    if contents.get("commit") == commit and (commit is not None or 1):
-        pass
+    if contents.get("commit") == commit:
+        reveal_type(commit)  # N: Revealed type is "builtins.str | None"