Remove the unnecessary python version matrix. (#26)

Author: benjyw

.github/workflows/pants.yaml

@@ -19,10 +19,6 @@ jobs:
     name: Perform CI Checks
     needs: org-check
     runs-on: ubuntu-20.04
-    strategy:
-      matrix:
-        # The python version to run Pants itself on.
-        python-version: [3.9]
     steps:
     - uses: actions/checkout@v3
     - uses: pantsbuild/actions/init-pants@v4-scie-pants