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_methods_and_attributes.py

@@ -4,7 +4,7 @@ import sys
 
 import pytest
 
-import env  # noqa: F401
+import env
 from pybind11_tests import ConstructorStats
 from pybind11_tests import methods_and_attributes as m
 
@@ -68,6 +68,9 @@ def test_methods_and_attributes():
     instance1.value = 100
     assert str(instance1) == "ExampleMandA[value=100]"
 
+    if env.GRAALPY:
+        pytest.skip("ConstructorStats is incompatible with GraalPy.")
+
     cstats = ConstructorStats.get(m.ExampleMandA)
     assert cstats.alive() == 2
     del instance1, instance2
@@ -316,6 +319,8 @@ def test_dynamic_attributes():
         instance.__dict__ = []
     assert str(excinfo.value) == "__dict__ must be set to a dictionary, not a 'list'"
 
+    if env.GRAALPY:
+        pytest.skip("ConstructorStats is incompatible with GraalPy.")
     cstats = ConstructorStats.get(m.DynamicClass)
     assert cstats.alive() == 1
     del instance
@@ -337,6 +342,7 @@ def test_dynamic_attributes():
 
 # https://foss.heptapod.net/pypy/pypy/-/issues/2447
 @pytest.mark.xfail("env.PYPY")
+@pytest.mark.skipif("env.GRAALPY", reason="Cannot reliably trigger GC")
 def test_cyclic_gc():
     # One object references itself
     instance = m.DynamicClass()