would this work?

matrix-action.yml

name: "Matrix experiment"

on:
  push:
  pull_request:
  workflow_dispatch:

defaults:
  run:
    shell: bash

jobs:
  define-excludes:
    runs-on: "ubuntu-latest"
    # Define any Django version you'd like to exclude from failing
    # tests in the D_EXCLUDE (can be expanded later to Python)
    # (not too sure what to do if there's more than 1)
    run: |
      echo 'D_EXCLUDE="4.0"'	>> $GITHUB_ENV
  tests:
    name: "py ${{ matrix.python-version }}; dj ${{ matrix.django-version}}"
    runs-on: "ubuntu-latest"
    needs: define-excludes
    strategy:
      fail-fast: false
      matrix:
        python-version:
          - "3.7"
          - "3.8"
          - "3.9"
          - "3.10"
        django-version:
          - "3.2"
          - "4.0"
    # We expect Django 4.0 to fail, so don't stop if it does.
    continue-on-error: ${{ matrix.django-version == $D_EXCLUDE }}

    steps:
      - name: "Fake tests"
        run: |
          echo "Python: ${{ matrix.python-version }}"
          echo "Django: ${{ matrix.django-version }}"
          # Django 4.0 doesn't pass yet...
          if [[ "${{ matrix.django-version }}" == $D_EXCLUDE ]]; then exit 17; fi
          echo "Success"  
      - name: "Process failure"
        if: ${{ failure() && matrix.django-version != $D_EXCLUDE }}
        run: |
       	  echo 'FAILED=1'	>> $GITHUB_ENV

  success:
    needs: tests
    name: "Test	Success?"
    steps:
      - run: |
      	  if $FAILED; exit 17; fi
          echo "Success"