add fail_silently attribute for BaseEmailBackend instances (#931)

Signed-off-by: Oleg Hoefling <oleg.hoefling@ionos.com>

django-stubs/core/mail/backends/base.pyi

@@ -6,6 +6,7 @@ from django.core.mail.message import EmailMessage
 _T = TypeVar("_T", bound="BaseEmailBackend")
 
 class BaseEmailBackend:
+    fail_silently: bool
     def __init__(self, fail_silently: bool = ..., **kwargs: Any) -> None: ...
     def open(self) -> Optional[bool]: ...
     def close(self) -> None: ...