Bump google-auth from 1.27.1 to 1.28.0 in /requirements (#16762)

Bumps [google-auth](https://github.com/googleapis/google-auth-library-python) from 1.27.1 to 1.28.0.
- [Release notes](https://github.com/googleapis/google-auth-library-python/releases)
- [Changelog](https://github.com/googleapis/google-auth-library-python/blob/master/CHANGELOG.md)
- [Commits](googleapis/google-auth-library-python@v1.27.1...v1.28.0)

Signed-off-by: dependabot[bot] <support@github.com>

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

requirements/prod.txt

@@ -480,9 +480,9 @@ zipp==3.4.1 \
 google-cloud-bigquery==2.12.0 \
     --hash=sha256:3a8e45ac90b491805e5a7938744bb2cca9dfebf28d7598dcfecfe379f3129159 \
     --hash=sha256:484bb733e5dd14bb82d28480a5d7f540b8ee59f081fcf32782546b717180d1b8
-google-auth==1.27.1 \
-    --hash=sha256:63a5636d7eacfe6ef5b7e36e112b3149fa1c5b5ad77dd6df54910459bcd6b89f \
-    --hash=sha256:d8958af6968e4ecd599f82357ebcfeb126f826ed0656126ad68416f810f7531e
+google-auth==1.28.0 \
+    --hash=sha256:dcaba3aa9d4e0e96fd945bf25a86b6f878fcb05770b67adbeb50a63ca4d28a5e \
+    --hash=sha256:9bd436d19ab047001a1340720d2b629eb96dd503258c524921ec2af3ee88a80e
 google-api-core==1.26.1 \
     --hash=sha256:c383206f0f87545d3e658c4f8dc3b18a8457610fdbd791a15757c5b42d1e0e7f \
     --hash=sha256:23b0df512c4cc8729793f8992edb350e3211f5fd0ec007afb1599864b421beef