Update validate-markdown.yaml

Author: ralfhandl

.github/workflows/validate-markdown.yaml

@@ -30,4 +30,4 @@ jobs:
     - name: Validate markdown
       run: npx --yes mdv versions/3.*.md
     - name: Lint markdown 3.0.4, 3.1.1, and later
-      run: npx --yes markdownlint-cli --config .markdownlint.yaml versions/3.0.4.md versions/3.1.[^0].md versions/3.[^01].*.md
+      run: npx --yes markdownlint-cli --config .markdownlint.yaml versions/3.0.4.md versions/3.1.[^0].md versions/3.[^01].*.md src/spec.md