Use modern syntax to get Actions output into GUI

Co-authored-by: Chuck Daniels <[email protected]>

.github/actions/install-pkg/action.yml

@@ -16,7 +16,7 @@ runs:
     - name: Display full python version
       shell: bash
       id: full-python-version
-      run: echo ::set-output name=version::$(python -c "import sys; print('-'.join(str(v) for v in sys.version_info))")
+      run: echo "{version}=$(python -c "import sys; print('-'.join(str(v) for v in sys.version_info))")" >> $GITHUB_OUTPUT
 
     - name: Install package and test dependencies
       shell: bash