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_virtual_functions.py

@@ -4,7 +4,7 @@ import sys
 
 import pytest
 
-import env  # noqa: F401
+import env
 
 m = pytest.importorskip("pybind11_tests.virtual_functions")
 from pybind11_tests import ConstructorStats  # noqa: E402
@@ -82,6 +82,9 @@ def test_override(capture, msg):
     """
     )
 
+    if env.GRAALPY:
+        pytest.skip("ConstructorStats is incompatible with GraalPy.")
+
     cstats = ConstructorStats.get(m.ExampleVirt)
     assert cstats.alive() == 3
     del ex12, ex12p, ex12p2
@@ -91,6 +94,7 @@ def test_override(capture, msg):
     assert cstats.move_constructions >= 0
 
 
+@pytest.mark.skipif("env.GRAALPY", reason="Cannot reliably trigger GC")
 def test_alias_delay_initialization1(capture):
     """`A` only initializes its trampoline class when we inherit from it
 
@@ -130,6 +134,7 @@ def test_alias_delay_initialization1(capture):
     )
 
 
+@pytest.mark.skipif("env.GRAALPY", reason="Cannot reliably trigger GC")
 def test_alias_delay_initialization2(capture):
     """`A2`, unlike the above, is configured to always initialize the alias
 
@@ -188,7 +193,7 @@ def test_alias_delay_initialization2(capture):
 
 # PyPy: Reference count > 1 causes call with noncopyable instance
 # to fail in ncv1.print_nc()
-@pytest.mark.xfail("env.PYPY")
+@pytest.mark.xfail("env.PYPY or env.GRAALPY")
 @pytest.mark.skipif(
     not hasattr(m, "NCVirt"), reason="NCVirt does not work on Intel/PGI/NVCC compilers"
 )