shell_plus_tests incompatible with Python 3.12

[michel-slm]

Tested on Fedora 39 with Python 3.12 beta 4

_________ CRTestCase.test_installed_apps_no_resolve_conflicts_function _________
TypeError: Can't instantiate abstract class CRNoFunction without an implementation for abstract method 'resolve_collisions'
                                                                  
During handling of the above exception, another exception occurred:

self = <tests.management.commands.shell_plus_tests.test_collision_resolver.CRTestCase testMethod=test_installed_apps_no_resolve_conflicts_function>         

    @override_settings(
        SHELL_PLUS_MODEL_IMPORTS_RESOLVER='tests.management.commands.shell_plus_tests.test_collision_resolver.CRNoFunction',
    )
    def test_installed_apps_no_resolve_conflicts_function(self):
        exception_msg = "Can't instantiate abstract class CRNoFunction with abstract methods resolve_collisions"
        if sys.version_info[:2] >= (3, 9):
            exception_msg = exception_msg.replace('methods', 'method')
>       with self.assertRaisesRegex(TypeError, exception_msg):
E       AssertionError: "Can't instantiate abstract class CRNoFunction with abstract method resolve_collisions" does not match "Can't instantiate abstract class CRNoFunction without an implementation for abstract method 'resolve_collisions'"