chore(deps): bump fastify/github-action-merge-dependabot

Bumps [fastify/github-action-merge-dependabot](https://github.com/fastify/github-action-merge-dependabot) from 3.12.0 to 3.15.0.
- [Release notes](https://github.com/fastify/github-action-merge-dependabot/releases)
- [Commits](fastify/github-action-merge-dependabot@30c3f8f...73ec4cb)

---
updated-dependencies:
- dependency-name: fastify/github-action-merge-dependabot
  dependency-version: 3.15.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

.github/workflows/dependabot-ci.yml

@@ -12,7 +12,7 @@ jobs:
       contents: write
 
     steps:
-      - uses: fastify/github-action-merge-dependabot@30c3f8f14a4f7b315ba38dbc1b793d27128fef82 # v3.12.0
+      - uses: fastify/github-action-merge-dependabot@73ec4cbb5e56df5591eae286972d5b2201ffe90f # v3.15.0
         with:
           use-github-auto-merge: true
           merge-method: squash