Bump docker from 5.0.2 to 5.0.3 in /tests (signalfx#1950)

Bumps [docker](https://github.com/docker/docker-py) from 5.0.2 to 5.0.3.
- [Release notes](https://github.com/docker/docker-py/releases)
- [Commits](docker/docker-py@5.0.2...5.0.3)

---
updated-dependencies:
- dependency-name: docker
  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

@@ -1,6 +1,6 @@
 PyYAML==6.0
 black==21.10b0
-docker==5.0.2
+docker==5.0.3
 hvac==0.11.2
 kubernetes==19.15.0
 mysql-connector-python==8.0.27