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

docs/contributing.md

@@ -82,6 +82,8 @@ A few notes-
 
 - Running the macOS integration tests requires _system installs_ of Python from python.org for all the versions that are tested. We won't attempt to install these when running locally, but you can do so manually using the URL in the error message that is printed when the install is not found.
 
+- The 'enable groups' run by default are just 'cpython-prerelease' and 'cpython-freethreading'. You can add other groups like pypy or graalpy by setting the [CIBW_ENABLE](options.md#enable) environment variable. On GitHub PRs, you can add a label to the PR to enable these groups.
+
 #### Running pytest directly
 
 More advanced users might prefer to invoke pytest directly. Set up a [dev environment](#setting-up-a-dev-environment), then,

docs/options.md

@@ -324,7 +324,7 @@ values are:
   are disabled by default as they can't be uploaded to PyPI and a PEP will most likely
   be required before this can happen.
 - `graalpy`: Enable GraalPy.
-
+- `all`: Enable all of the above.
 
 !!! caution
     `cpython-prerelease` is provided for testing purposes only. It is not