Fixes issue #3788 (#3796)

* Reproducer for https://github.com/pybind/pybind11/issues/3788

Expected to build & run as-is. Uncommenting reproduces the infinite recursion.

* Moving try_as_void_ptr_capsule() to the end of load_impl()

* Moving new test into the existing test_class_sh_void_ptr_capsule

* Experiment

* Remove comments and simplify the test cases.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci



Co-authored-by: Ralf W. Grosse-Kunstleve <rwgk@google.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>