gc: fix arg name, mark positional-only args (#3760)

tests/stubtest_whitelists/py37.txt

@@ -45,7 +45,6 @@ email.message.MIMEPart.as_string
 email.mime.message.MIMEMessage.__init__
 email.mime.text.MIMEText.__init__
 enum.Enum._generate_next_value_
-gc.collect
 gettext.NullTranslations.npgettext
 gettext.NullTranslations.pgettext
 gettext.dnpgettext

tests/stubtest_whitelists/py38.txt

@@ -114,9 +114,6 @@ fcntl.flock
 fcntl.ioctl
 fcntl.lockf
 functools.partialmethod.__get__
-gc.collect
-gc.is_tracked
-gc.set_debug
 gettext.install
 gettext.translation
 hmac.compare_digest