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_operator_overloading.py

@@ -2,10 +2,12 @@ from __future__ import annotations
 
 import pytest
 
+import env  # noqa: F401
 from pybind11_tests import ConstructorStats
 from pybind11_tests import operators as m
 
 
+@pytest.mark.xfail("env.GRAALPY", reason="TODO should get fixed on GraalPy side")
 def test_operator_overloading():
     v1 = m.Vector2(1, 2)
     v2 = m.Vector(3, -1)
@@ -83,6 +85,7 @@ def test_operator_overloading():
     assert cstats.move_assignments == 0
 
 
+@pytest.mark.xfail("env.GRAALPY", reason="TODO should get fixed on GraalPy side")
 def test_operators_notimplemented():
     """#393: need to return NotSupported to ensure correct arithmetic operator behavior"""