Add django.db.models.functions.Collate (#1143)

django-stubs/db/models/functions/__init__.pyi

@@ -1,5 +1,6 @@
 from .comparison import Cast as Cast
 from .comparison import Coalesce as Coalesce
+from .comparison import Collate as Collate
 from .comparison import Greatest as Greatest
 from .comparison import Least as Least
 from .comparison import NullIf as NullIf

django-stubs/db/models/functions/comparison.pyi

@@ -8,6 +8,10 @@ class Cast(Func):
     def __init__(self, expression: Any, output_field: Union[str, Field]) -> None: ...
 
 class Coalesce(Func): ...
+
+class Collate(Func):
+    def __init__(self, expression: Any, collation: str) -> None: ...
+
 class Greatest(Func): ...
 
 class JSONObject(Func):