GitHub Action: Bump microsoft/mu_devops/.github/workflows/AutoMerger.yml

Bumps [microsoft/mu_devops/.github/workflows/AutoMerger.yml](https://github.com/microsoft/mu_devops) from 13.0.0 to 18.0.3.
- [Release notes](https://github.com/microsoft/mu_devops/releases)
- [Commits](microsoft/mu_devops@v13.0.0...v18.0.3)

---
updated-dependencies:
- dependency-name: microsoft/mu_devops/.github/workflows/AutoMerger.yml
  dependency-version: 18.0.3
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/auto-merge.yml

@@ -32,5 +32,5 @@ jobs:
 
     if: |
       github.event.pull_request.user.login == 'dependabot[bot]' || github.event.pull_request.user.login == 'uefibot'
-    uses: microsoft/mu_devops/.github/workflows/AutoMerger.yml@v13.0.0
+    uses: microsoft/mu_devops/.github/workflows/AutoMerger.yml@v18.0.3
     secrets: inherit