♻️ simplify reusable Python CI workflow (cda-tum#591)

## Description

This PR simplifies the CI pipeline a little by combining two jobs into
one and, as a consequence, saving one runner that has to spin up just to
run a single command.

## Checklist:

<!---
This checklist serves as a reminder of a couple of things that ensure
your pull request will be merged swiftly.
-->

- [x] The pull request only contains commits that are related to it.
- [x] I have added appropriate tests and documentation.
- [x] I have made sure that all CI jobs on GitHub pass.
- [x] The pull request introduces no new warnings and follows the
project's style guidelines.

---------

Signed-off-by: burgholzer <burgholzer@me.com>

Author: burgholzer

.github/workflows/reusable-python-ci.yml

@@ -43,18 +43,11 @@ jobs:
         uses: rui314/setup-mold@v1
       - uses: hynek/build-and-inspect-python-package@v2
         id: baipp
-    outputs:
-      python-versions: ${{ steps.baipp.outputs.supported_python_classifiers_json_array }}
-
-  max-python-version:
-    name: 🐍 Determine maximum supported Python version
-    needs: dist
-    runs-on: ubuntu-latest
-    steps:
-      # use jq to get the last element of the array
-      - run: echo "max-python-version=$(echo '${{ needs.dist.outputs.python-versions }}' | jq --raw-output '.[-1]')" >> $GITHUB_OUTPUT
+      - name: 🐍 Determine maximum supported Python version
+        run: echo "max-python-version=$(echo '${{ steps.baipp.outputs.supported_python_classifiers_json_array }}' | jq --raw-output '.[-1]')" >> $GITHUB_OUTPUT
         id: max-python-version
     outputs:
+      python-versions: ${{ steps.baipp.outputs.supported_python_classifiers_json_array }}
       max-python-version: ${{ steps.max-python-version.outputs.max-python-version }}
 
   python-tests-ubuntu:
@@ -75,17 +68,17 @@ jobs:
 
   python-tests-macos:
     name: 🍎 ${{ matrix.python-version }} ${{ matrix.runs-on }}
-    needs: [dist, max-python-version]
+    needs: [dist]
     strategy:
       fail-fast: false
       matrix:
         python-version:
           - ${{ fromJson(needs.dist.outputs.python-versions)[0] }}
-          - ${{ needs.max-python-version.outputs.max-python-version }}
+          - ${{ needs.dist.outputs.max-python-version }}
         runs-on: [macos-13] # test Intel architecture
         include:
           - runs-on: macos-14 # test Apple Silicon architecture
-            python-version: ${{ needs.max-python-version.outputs.max-python-version }} # testing Apple Silicon on 3.8 is blocked by https://github.com/actions/setup-python/issues/808
+            python-version: ${{ needs.dist.outputs.max-python-version }} # testing Apple Silicon on 3.8 is blocked by https://github.com/actions/setup-python/issues/808
     uses: ./.github/workflows/reusable-python-tests.yml
     with:
       runs-on: ${{ matrix.runs-on }}
@@ -97,13 +90,13 @@ jobs:
 
   python-tests-windows:
     name: 🏁 ${{ matrix.python-version }}
-    needs: [dist, max-python-version]
+    needs: [dist]
     strategy:
       fail-fast: false
       matrix:
         python-version:
           - ${{ fromJson(needs.dist.outputs.python-versions)[0] }}
-          - ${{ needs.max-python-version.outputs.max-python-version }}
+          - ${{ needs.dist.outputs.max-python-version }}
     uses: ./.github/workflows/reusable-python-tests.yml
     with:
       runs-on: windows-latest
@@ -115,13 +108,13 @@ jobs:
 
   minimums:
     name: 🔧 Minimums
-    needs: [dist, max-python-version]
+    needs: [dist]
     strategy:
       fail-fast: false
       matrix:
         python-version:
           - ${{ fromJson(needs.dist.outputs.python-versions)[0] }}
-          - ${{ needs.max-python-version.outputs.max-python-version }}
+          - ${{ needs.dist.outputs.max-python-version }}
     uses: ./.github/workflows/reusable-python-minimums.yml
     with:
       runs-on: ubuntu-latest