Add yamllint

Author: jeffwidman

.github/workflows/ci.yml

@@ -29,6 +29,9 @@ jobs:
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
 
+      # yamllint is installed in GitHub Actions base runner image: https://github.com/adrienverge/yamllint/pull/588
+      - run: yamllint .
+
       - uses: actions/setup-go@0aaccfd150d50ccaeb58ebd88d36e91967a5f35b # v5.4.0
         with:
           go-version-file: go.mod