revert test matrix to manual

See MDAnalysis/cookiecutter-mdakit#111

.github/workflows/gh-ci.yaml

@@ -23,32 +23,21 @@ defaults:
     shell: bash  -l {0} 
 
 jobs:
-  environment-config:
-    runs-on: ubuntu-latest
-    outputs:
-      stable-python-version: ${{ steps.get-compatible-python.outputs.stable-python }}
-      python-matrix: ${{ steps.get-compatible-python.outputs.python-versions }}
-    steps:
-      - uses: actions/setup-python@v4
-        with:
-          python-version: "3.11"
-
-      - id: get-compatible-python
-        uses: MDAnalysis/mdanalysis-compatible-python@main
-        with:
-          release: "latest"
-
   main-tests:
     if: "github.repository == 'MDAnalysis/mdgeomkit'"
-    needs: environment-config
     runs-on: ${{ matrix.os }}
     strategy:
         fail-fast: false
         matrix:
           os: [macOS-latest, ubuntu-latest, windows-latest]
-          python-version: ${{ fromJSON(needs.environment-config.outputs.python-matrix) }}
           mdanalysis-version: ["latest", "develop"]
-
+          python-version: ["3.10", "3.11", "3.12"]
+          exclude:
+            # Entries here exclude particular combinations of the matrix
+            # Edit or remove as particular combinations come into or out of date
+            # Below we exclude runs with the latest release and Python 3.12
+            - mdanalysis-version: "latest"
+              python-version: "3.12"
     steps:
     - uses: actions/checkout@v4