Mark regex as completed (#9214)

stubs/regex/@tests/stubtest_allowlist.txt

@@ -1,6 +1,18 @@
-# These classes are defined in regex/_regex.c and are returned by the public API functions.
-# The stubs are defined in regex/_regex.pyi but these classes aren't present at runtime.
-regex._regex.Match
-regex._regex.Pattern
-regex._regex.Scanner
+# Not exported in C modules:
 regex._regex.Splitter
+regex._regex.Scanner
+
+# Implementation details:
+regex._regex.compile
+regex._regex.copyright
+regex._regex.fold_case
+regex._regex.get_all_cases
+regex._regex.get_code_size
+regex._regex.get_expand_on_folding
+regex._regex.get_properties
+regex._regex.has_property_value
+regex._regex.CODE_SIZE
+regex._regex.MAGIC
+
+# Tests:
+regex.test_regex