ci: reduce usage and add Python 3.12 beta

With 3.12 beta, there are 7 Python versions to test, which is making the
test matrix too large. To reduce the amount of CI test runs that occur,
by default we will only run 2: the oldest and newest released Python
versions. To further reduce the CI test runs, we will eliminate CI runs
when a branch is pushed (only main will be tested).

The "ci" action becomes a reusable workflow, which gets called by other
possible workflows:

1. pull_request.yml: On pull request, only the 2 default Python versions
   are tested.  The "test-all-python-versions" label can be applied to
   pull requests to override this.
2. push.yml: On push to main, all Python versions are tested.
3. vmtest-build.yml: After the vmtest kernels are built
4. On manual request: the user has the option to specify

Signed-off-by: Stephen Brennan <stephen@brennan.io>

.github/workflows/ci.yml

@@ -1,6 +1,20 @@
 name: CI
 
-on: [push, pull_request]
+on:
+  workflow_dispatch:
+    inputs:
+      test_all_python_versions:
+        description: "Run tests on all Python versions"
+        type: boolean
+        default: false
+        required: true
+  workflow_call:
+    inputs:
+      test_all_python_versions:
+        description: "Run tests on all Python versions"
+        type: boolean
+        default: false
+        required: true
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
@@ -13,7 +27,9 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        python-version: ['3.11', '3.10', '3.9', '3.8', '3.7', '3.6']
+        python-version: ${{ inputs.test_all_python_versions
+                            && fromJSON('["3.12", "3.11", "3.10", "3.9", "3.8", "3.7", "3.6"]')
+                            || fromJSON('["3.11", "3.6"]')}}
         cc: [gcc, clang]
       fail-fast: false
     env:
@@ -25,6 +41,7 @@ jobs:
         uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python-version }}
+          allow-prereleases: true
       - name: Install dependencies
         run: |
           sudo apt-get update

.github/workflows/pull_request.yml

@@ -0,0 +1,16 @@
+name: Pull Request CI
+
+on:
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - labeled
+
+jobs:
+  test:
+    uses: ./.github/workflows/ci.yml
+    if: ${{ github.event.action != 'labeled' || github.event.label.name == 'test-all-python-versions' }}
+    with:
+      test_all_python_versions: ${{ contains(github.event.pull_request.labels.*.name, 'test-all-python-versions') }}

.github/workflows/push.yml

@@ -0,0 +1,12 @@
+name: Main Branch Push CI
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  test:
+    uses: ./.github/workflows/ci.yml
+    with:
+      test_all_python_versions: true

.github/workflows/vmtest-build.yml

@@ -36,3 +36,8 @@ jobs:
           name: kernel-build-logs
           path: build/vmtest/kbuild/*.log
           if-no-files-found: ignore
+  test:
+    needs: build
+    uses: ./.github/workflows/ci.yml
+    with:
+      test_all_python_versions: true