Adds checkout action for pull requests

Adds a checkout action to the workflow to ensure the code is available for pull request events.

Author: arturcic

.github/workflows/mkdocs.yml

@@ -23,6 +23,10 @@ jobs:
         if: github.event_name == 'push'
         with:
           token: ${{ secrets.PUSH_GITHUB_TOKEN }}
+      -
+        name: Checkout
+        uses: actions/checkout@v5
+        if: github.event_name == 'pull_request'
       -
         name: Setup .NET SDK
         uses: actions/setup-dotnet@v5