Bump proto-plus from 1.20.1 to 1.20.3 (#133)

Bumps [proto-plus](https://github.com/googleapis/proto-plus-python) from 1.20.1 to 1.20.3.
- [Release notes](https://github.com/googleapis/proto-plus-python/releases)
- [Changelog](https://github.com/googleapis/proto-plus-python/blob/main/CHANGELOG.md)
- [Commits](googleapis/proto-plus-python@v1.20.1...v1.20.3)

---
updated-dependencies:
- dependency-name: proto-plus
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

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

requirements.txt

@@ -14,7 +14,7 @@ grpcio-status==1.43.0
 idna==3.3
 packaging==21.3
 pip==22.0.3
-proto-plus==1.20.1
+proto-plus==1.20.3
 protobuf==3.19.4
 pyasn1==0.4.8
 pyasn1-modules==0.2.8