chore(deps): bump google-cloud-core from 2.5.0 to 2.6.0

Bumps [google-cloud-core](https://github.com/googleapis/google-cloud-python) from 2.5.0 to 2.6.0.
- [Release notes](https://github.com/googleapis/google-cloud-python/releases)
- [Changelog](https://github.com/googleapis/google-cloud-python/blob/main/packages/google-cloud-documentai/CHANGELOG.md)
- [Commits](googleapis/google-cloud-python@google-cloud-core-v2.5.0...google-cloud-core-v2.6.0)

---
updated-dependencies:
- dependency-name: google-cloud-core
  dependency-version: 2.6.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements.txt

@@ -117,7 +117,7 @@ google-cloud-appengine-logging==1.8.0
     # via google-cloud-logging
 google-cloud-audit-log==0.4.0
     # via google-cloud-logging
-google-cloud-core==2.5.0
+google-cloud-core==2.6.0
     # via
     #   -r requirements.in
     #   google-cloud-logging