[3.14] gh-145557: Check ctypes is available in test_external_inspection (GH-145558) (#145565)

gh-145557: Check ctypes is available in test_external_inspection (GH-145558)

Currently TestGetStackTrace.test_self_trace_after_ctypes_import() will fail if
the _ctypes extension is not built.  Make it match test_ctypes by skipping
the test in that case.
(cherry picked from commit 7232883adfc28f94a62d2e79c897db59711702d7)

Co-authored-by: Alex Malyshev <lex.malyshev@gmail.com>