[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.

Python/ceval.c

@@ -5377,6 +5377,8 @@ prtrace(PyThreadState *tstate, PyObject *v, const char *str)
     }
     printf("\n");
     PyErr_Restore(type, value, traceback);
+    // gh-91924: PyObject_Print() can indirectly set lltrace to 0
+    lltrace = 1;
     return 1;
 }
 #endif