Test enable groups as specified by PR labels (#2357)

* Allow CIBW_ENABLE to control the wheels built in testing

* Set CIBW_ENABLE using PR labels

* Add docs

* Build everything on the main branch

* Add CIBW_ENABLE=all option

This was mostly for use in the `main` building case, because otherwise it's maybe a bit too easy to forget to update this file when adding an enable group

* Remove dead code

* Make unit tests robust to the value of CIBW_ENABLE

* Fix tests that explicitly choose pypy

* Fix test expectation

* Don't expect impossible wheels in expected_wheels

* Simplify logic in expected_wheels

* CircleCI- run with CIBW_ENABLE=all only on the main branch

* Azure pipelines - run with CIBW_ENABLE=all on main branch

* Update gitlab to run CIBW_ENABLE=all on main

* Set CIBW_ENABLE=all on travis - it only runs on main anyway

* Fix job name error on CircleCI

* Fix tests for graalpy

* Update the test configuration to use the label

* Remove duplication of default value. Make it affect sample build too

* Move the action to after deps are installed

* GraalPy workaround for this assumption

* Make unit test resilient to changing CIBW_ENABLE

.github/workflows/test.yml

@@ -6,6 +6,11 @@ on:
       - main
       - 2.x
   pull_request:
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - labeled
     paths-ignore:
       - 'docs/**'
       - .pre-commit-config.yaml
@@ -68,6 +73,26 @@ jobs:
       run: |
         uv sync --no-dev --group test
 
+    - uses: joerick/pr-labels-action@v1.0.9
+    - name: Set CIBW_ENABLE
+      shell: bash
+      run: |
+        if [[ "${{ github.ref_name }}" == "main" ]]; then
+          CIBW_ENABLE=all
+        else
+          # get the default CIBW_ENABLE value from the test module
+          CIBW_ENABLE=$(uv run --no-sync python -c 'import sys, test.conftest as c; sys.stdout.write(c.DEFAULT_CIBW_ENABLE)')
+
+          # if this is a PR, check for labels
+          if [[ -n "$GITHUB_PR_LABEL_CI_PYPY" ]]; then
+            CIBW_ENABLE+=" pypy"
+          fi
+          if [[ -n "$GITHUB_PR_LABEL_CI_GRAALPY" ]]; then
+            CIBW_ENABLE+=" graalpy"
+          fi
+        fi
+        echo "CIBW_ENABLE=${CIBW_ENABLE}" >> $GITHUB_ENV
+
     - name: Generate a sample project
       run: |
         uv run --no-sync -m test.test_projects test.test_0_basic.basic_project sample_proj
@@ -80,7 +105,6 @@ jobs:
       env:
         CIBW_ARCHS_MACOS: x86_64 universal2 arm64
         CIBW_BUILD_FRONTEND: 'build[uv]'
-        CIBW_ENABLE: "cpython-prerelease cpython-freethreading pypy graalpy"
 
     - name: Run a sample build (GitHub Action, only)
       uses: ./