Update BaseCommand.requires_system_checks for django >=3.2 (#600)

- the documentation for this specific change in django can be seen at https://docs.djangoproject.com/en/3.2/howto/custom-management-commands/#django.core.management.BaseCommand.requires_system_checks

django-stubs/core/management/base.pyi

@@ -4,6 +4,7 @@ from typing import Any, Callable, List, Optional, Union, Tuple
 
 from django.apps.config import AppConfig
 from django.core.management.color import Style
+from django.core.checks import Tags
 
 class CommandError(Exception): ...
 class SystemCheckError(CommandError): ...
@@ -38,7 +39,7 @@ class BaseCommand:
     help: str = ...
     output_transaction: bool = ...
     requires_migrations_checks: bool = ...
-    requires_system_checks: bool = ...
+    requires_system_checks: Union[bool, List[Tags], Tuple[Tags, ...], str]  = ...
     base_stealth_options: Tuple[str, ...] = ...
     stealth_options: Tuple[str, ...] = ...
     stdout: OutputWrapper = ...