fix: replace now deprecated set-env with new GitHub Env file

Author: Pankaj Agrawal

.github/workflows/docs.yml

@@ -18,9 +18,8 @@ jobs:
       - name: Capture branch and tag
         id: branch_name
         run: |
-          echo ::set-env name=SOURCE_BRANCH::${GITHUB_REF#refs/heads/}
-          echo ::set-env name=SOURCE_TAG::${GITHUB_REF#refs/tags/}
-
+          echo "SOURCE_BRANCH=${GITHUB_REF#refs/heads/}" >> $GITHUB_ENV
+          echo "SOURCE_TAG=${GITHUB_REF#refs/tags/}" >> $GITHUB_ENV
       - name: install dependencies
         run: make dev-docs
       - name: Build docs website