Bump protobuf from 3.19.1 to 3.19.3 in /tests (signalfx#2074)

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 3.19.1 to 3.19.3.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/master/generate_changelog.py)
- [Commits](protocolbuffers/protobuf@v3.19.1...v3.19.3)

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

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

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

tests/requirements.txt

@@ -5,7 +5,7 @@ hvac==0.11.2
 kubernetes==21.7.0
 mysql-connector-python==8.0.27
 netifaces==0.11.0
-protobuf==3.19.1
+protobuf==3.19.3
 psutil==5.9.0
 pylint==2.12.2
 pytest-html==3.1.1