Bump google-auth from 2.4.1 to 2.6.0 in /requirements (#18731)

Bumps [google-auth](https://github.com/googleapis/google-auth-library-python) from 2.4.1 to 2.6.0.
- [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](https://github.com/googleapis/google-auth-library-python/compare/v2.4.1...v2.6.0)

---
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>

requirements/prod.txt

@@ -395,9 +395,9 @@ zipp==3.7.0 \
 google-cloud-bigquery==2.32.0 \
     --hash=sha256:09588ffdf0ae92673d980cdade81a371ff1852c043bebd8bab68a47fd69d8a1f \
     --hash=sha256:f3863ac4293f0a4585e44461d82b91f9239721ef33fc9575d401b4da7dc127bd
-google-auth==2.4.1 \
-    --hash=sha256:e914f186f2ef0b78a1cfeb6dcd1243c425ddeef3a13e6b39af5b0eb356a3b580 \
-    --hash=sha256:baefcc6fc5c337e191929be749622cdfe5a5e063bc2fb64f17effdce0fa569cd
+google-auth==2.6.0 \
+    --hash=sha256:218ca03d7744ca0c8b6697b6083334be7df49b7bf76a69d555962fd1a7657b5f \
+    --hash=sha256:ad160fc1ea8f19e331a16a14a79f3d643d813a69534ba9611d2c80dc10439dad
 google-api-core==2.4.0 \
     --hash=sha256:58e2c1171a3d51778bf4e428fbb4bf79cbd05007b4b44deaa80cf73c80eebc0f \
     --hash=sha256:ba8787b7c61632cd0340f095e1c036bef9426b2594f10afb290ba311ae8cb2cb