Replace deprecated ::set-output (#337)

As per the deprecation warning and explanation at
https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

Author: nodeg

.github/workflows/test-python.yml

@@ -57,7 +57,7 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Get full Python version
       id: full-python-version
-      run: echo ::set-output name=version::$(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: Bootstrap poetry
       run: |
         curl -sL https://install.python-poetry.org | python - -y ${{ matrix.bootstrap-args }}