ci: Use GITHUB_OUTPUT envvar instead of set-output command (#1659)

`save-state` and `set-output` commands used in GitHub Actions are deprecated and [GitHub recommends using environment files](https://github.blog/changelog/2023-07-24-github-actions-update-on-save-state-and-set-output-commands/).

This PR updates the usage of `set-output` to `$GITHUB_OUTPUT`

Instructions for envvar usage from GitHub docs:

https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-output-parameter

Author: arunsathiya

.github/workflows/update-Dockerfiles.yml

@@ -118,7 +118,7 @@ jobs:
           git add "**/*Dockerfile"
           git commit -m "chore: ASP.NET Core version update in Dockerfiles"
           git push origin $branch
-          echo "::set-output name=BRANCH::$branch"
+          echo "BRANCH=$branch" >> $GITHUB_OUTPUT
 
       # Create a Pull Request from the pushed branch
       - name: Pull Request