ci: Update the name of python matrix to be consistent with other repos (GoogleCloudPlatform#224)

Author: chizhg

.github/workflows/conformance.yml

@@ -5,7 +5,7 @@ jobs:
     runs-on: ubuntu-18.04
     strategy:
       matrix:
-        python-version: ['3.8', '3.9', '3.10', '3.11']
+        python: ['3.8', '3.9', '3.10', '3.11']
     steps:
     - name: Harden Runner
       uses: step-security/harden-runner@18bf8ad2ca49c14cbb28b91346d626ccfb00c518 # v2.1.0
@@ -18,7 +18,7 @@ jobs:
     - name: Setup Python
       uses: actions/setup-python@75f3110429a8c05be0e1bf360334e4cced2b63fa # v2.3.3
       with:
-        python-version: ${{ matrix.python-version }}
+        python-version: ${{ matrix.python }}
 
     - name: Install the framework
       run: python -m pip install -e .