Pin markdownlint-cli version to 0.45.0 in GitHub workflow (dotnet#62034)

* Initial plan for issue

* Pin markdownlint-cli version to 0.45.0

Co-authored-by: captainsafia <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: captainsafia <[email protected]>

Author: Copilot

.github/workflows/markdownlint.yml

@@ -24,5 +24,5 @@ jobs:
     - name: Run Markdownlint
       run: |
         echo "::add-matcher::.github/workflows/markdownlint-problem-matcher.json"
-        npm i -g markdownlint-cli
+        npm i -g markdownlint-cli@0.45.0
         markdownlint "docs/**/*.md"