tests: always disable on the nogil build (#5701)

* docs: fix docs on visibilty preset hidden

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* tests: always disable on the nogil build

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* style: pre-commit fixes

* docs: mention skip reason in comment

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

---------

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

tests/test_gil_scoped.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 import multiprocessing
 import sys
+import sysconfig
 import threading
 import time
 
@@ -10,8 +11,11 @@ import pytest
 import env
 from pybind11_tests import gil_scoped as m
 
+# Test collection seems to hold the gil
+# These tests have rare flakes in nogil; since they
+# are testing the gil, they are skipped at the moment.
 skipif_not_free_threaded = pytest.mark.skipif(
-    not getattr(sys, "_is_gil_enabled", lambda: True)(),
+    sysconfig.get_config_var("Py_GIL_DISABLED"),
     reason="Flaky without the GIL",
 )
 

tools/pybind11Config.cmake.in

@@ -94,7 +94,7 @@ you can either use the basic targets, or use the FindPython tools:
   target_link_libraries(MyModule2 PUBLIC pybind11::headers)
   set_target_properties(MyModule2 PROPERTIES
                                   INTERPROCEDURAL_OPTIMIZATION ON
-                                  CXX_VISIBILITY_PRESET ON
+                                  CXX_VISIBILITY_PRESET hidden
                                   VISIBILITY_INLINES_HIDDEN ON)
 
 If you build targets yourself, you may be interested in stripping the output