Add explicit test with Iterable that is not a Sequence for __all__

Author: sterliakov

test-data/unit/check-modules.test

@@ -433,6 +433,13 @@ __all__ = 1  # E: Type of __all__ must be "Sequence[str]", not "int"
 reveal_type(__all__)  # N: Revealed type is "builtins.int"
 [builtins fixtures/module_all.pyi]
 
+[case testAllMustBeSequenceStr3]
+import typing
+__all__ = set()  # E: Need type annotation for "__all__" (hint: "__all__: set[<type>] = ...") \
+                 # E: Type of __all__ must be "Sequence[str]", not "set[Any]"
+reveal_type(__all__)  # N: Revealed type is "builtins.set[Any]"
+[builtins fixtures/set.pyi]
+
 [case testModuleAllEmptyList]
 __all__ = []
 reveal_type(__all__)  # N: Revealed type is "builtins.list[builtins.str]"