change deprecated use of ::set-output to environment file

Author: joeljonsson

.github/workflows/deploy-docs.yml

@@ -122,7 +122,7 @@ jobs:
       - name: Get version
         id: get_version
         run: |
-          echo ::set-output name=VERSION_TAG::${GITHUB_REF#refs/tags/}
+          echo "VERSION_TAG=${GITHUB_REF#refs/tags/}" >> $GITHUB_OUTPUT
 
       - name: Deploy documentation
         if: ${{ (env.BRANCH_NAME == 'master') || (env.BRANCH_NAME == 'develop') }}