Add support for GraalPy (#5380)

* Initial support for GraalPy

* Mark tests that currently fail on GraalPy with xfail

* Add graalpy to CI

* Limit test deps on graalpy to available binary wheels

* Skip cmake test installed_function on GraalPy

CMake won't find libpython on GraalPy, it either fails or silently picks
CPython's libpython.

* Factor out setting function docstrings into a macro

* Try to narrow down skipped tests

tests/test_callbacks.cpp

@@ -270,7 +270,7 @@ TEST_SUBMODULE(callbacks, m) {
     m.add_object("custom_function", PyCFunction_New(custom_def, rec_capsule.ptr()));
 
     // This test requires a new ABI version to pass
-#if PYBIND11_INTERNALS_VERSION > 4
+#if PYBIND11_INTERNALS_VERSION > 4 && !defined(GRAALVM_PYTHON)
     // rec_capsule with nullptr name
     py::capsule rec_capsule2(std::malloc(1), [](void *data) { std::free(data); });
     m.add_object("custom_function2", PyCFunction_New(custom_def, rec_capsule2.ptr()));