Bump google-cloud-datastore from 2.10.0 to 2.21.0

Bumps [google-cloud-datastore](https://github.com/googleapis/python-datastore) from 2.10.0 to 2.21.0.
- [Release notes](https://github.com/googleapis/python-datastore/releases)
- [Changelog](https://github.com/googleapis/python-datastore/blob/main/CHANGELOG.md)
- [Commits](googleapis/python-datastore@v2.10.0...v2.21.0)

---
updated-dependencies:
- dependency-name: google-cloud-datastore
  dependency-version: 2.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 Babel
-google-cloud-datastore==2.10.0
+google-cloud-datastore==2.21.0
 humanize
 img2pdf
 Logbook