Bump trillian-opensource-ci/mysql5 (#3120)

Bumps trillian-opensource-ci/mysql5 from `edf7def` to `f45c849`.

---
updated-dependencies:
- dependency-name: trillian-opensource-ci/mysql5
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

examples/deployment/docker/db_server/Dockerfile

@@ -1,4 +1,4 @@
-FROM gcr.io/trillian-opensource-ci/mysql5:5.7@sha256:edf7defdd589073b6659ae07e84be82af8362f30ffa4091c5ed422d6a55c50c1
+FROM gcr.io/trillian-opensource-ci/mysql5:5.7@sha256:f45c849cf48c49c75cf9cbdf1ef68cecd7fd3fb9612325909a9eee1b2d1c462e
 
 # Patch the OS-level packages and remove unneeded dependencies.
 ENV DEBIAN_FRONTEND=noninteractive