Bump google-auth from 2.15.0 to 2.16.0 in /tests (#3419)

Bumps [google-auth](https://github.com/googleapis/google-auth-library-python) from 2.15.0 to 2.16.0.
- [Release notes](https://github.com/googleapis/google-auth-library-python/releases)
- [Changelog](https://github.com/googleapis/google-auth-library-python/blob/main/CHANGELOG.md)
- [Commits](googleapis/google-auth-library-python@v2.15.0...v2.16.0)

---
updated-dependencies:
- dependency-name: google-auth
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

tests/requirements.txt

@@ -131,9 +131,9 @@ flaky==3.7.0 \
 forcediphttpsadapter==1.0.2 \
     --hash=sha256:f7582b34aaa6ab6b17f69ab1abbfe67097b952ed0682b758b5e01e18fe24433e
     # via -r requirements.txt
-google-auth==2.15.0 \
-    --hash=sha256:6897b93556d8d807ad70701bb89f000183aea366ca7ed94680828b37437a4994 \
-    --hash=sha256:72f12a6cfc968d754d7bdab369c5c5c16032106e52d32c6dfd8484e4c01a6d1f
+google-auth==2.16.0 \
+    --hash=sha256:5045648c821fb72384cdc0e82cc326df195f113a33049d9b62b74589243d2acc \
+    --hash=sha256:ed7057a101af1146f0554a769930ac9de506aeca4fd5af6543ebe791851a9fbd
     # via
     #   -r requirements.txt
     #   kubernetes