[3.10] gh-91924: Fix __ltrace__ for non-UTF-8 stdout encoding (#93214)

Fix __ltrace__ debug feature if the stdout encoding is not UTF-8.

If the stdout encoding is not UTF-8, the first call to
lltrace_resume_frame() indirectly sets lltrace to 0 when calling
unicode_check_encoding_errors() which calls
encodings.search_function().

Add test_lltrace.test_lltrace() test.