devel/py-strawberry-graphql: Update to 0.237.2

• Belatedly add CONFLICTS_INSTALL while I'm here, because the port has now also had devel/py-dj50-strawberry-graphql as Django 5.0 counterpart since 9dcfcfc7df21.

Changelog since 0.235.2:

https://github.com/strawberry-graphql/strawberry/blob/0.237.2/CHANGELOG.md