Skip the bisection when the start and end hash are the same (#2044)

Summary:
Nightly releases could be built from the same commit on the main branch (e.g. [20231112](pytorch/pytorch@63a5a14) and [20231113](pytorch/pytorch@a45a8bf)).

If it happens, we can just skip the bisection because there is no code change.

Pull Request resolved: #2044

Test Plan: https://github.com/pytorch/benchmark/actions/runs/6906833305

Reviewed By: aaronenyeshi

Differential Revision: D51429932

Pulled By: xuzhao9

fbshipit-source-id: 1ee006f12006689f53483bbf8beb764557e024ca

bisection.py

@@ -425,6 +425,10 @@ def output(self):
                                     bisect_config=bisect_config,
                                     output_json=args.output,
                                     debug=args.debug)
+    if start_hash == end_hash:
+        print(f"Start and end hash are the same: {start_hash}. Skip bisection")
+        bisection.output()
+        exit(0)
     assert bisection.prep(), "The working condition of bisection is not satisfied."
     print("Preparation steps ok. Commit to bisect: " + " ".join([str(x) for x in bisection.target_repo.commits]))
     bisection.run()