Fix interfaces with duplicate directives

strawberry/permission.py

@@ -158,9 +158,14 @@ def __init__(
     def apply(self, field: StrawberryField) -> None:
         """Applies all of the permission directives to the schema and sets up silent permissions."""
         if self.use_directives:
-            field.directives.extend(
+            # Dedupe multiple directives
+            # https://github.com/strawberry-graphql/strawberry/issues/3596
+            permission_directives = {
                 p.schema_directive for p in self.permissions if p.schema_directive
-            )
+            }
+            existing_field_directives = set(field.directives)
+            extend_directives = permission_directives - existing_field_directives
+            field.directives.extend(extend_directives)
         # We can only fail silently if the field is optional or a list
         if self.fail_silently:
             if isinstance(field.type, StrawberryOptional):