Add __all__ (#13704)

stubs/PyYAML/@tests/stubtest_allowlist.txt

@@ -1,17 +1,3 @@
-# TODO: missing from stub
-yaml.composer.__all__
-yaml.constructor.__all__
-yaml.dumper.__all__
-yaml.emitter.__all__
-yaml.error.__all__
-yaml.loader.__all__
-yaml.parser.__all__
-yaml.reader.__all__
-yaml.representer.__all__
-yaml.resolver.__all__
-yaml.scanner.__all__
-yaml.serializer.__all__
-
 # yaml._yaml is for backwards compatibility so none of it matters anyway
 yaml._yaml.__test__