Add explicit types to guard against join-vs-union changes

Author: sterliakov

test-data/unit/check-functions.test

@@ -3705,6 +3705,8 @@ class P(Protocol):
 
 def foo(x: P, y: P) -> None: ...
 
-foo(*[0, ''])  # E: Argument 1 to "foo" has incompatible type "*list[object]"; expected "P"
-foo(**{'x': 0, 'y': ''})  # E: Argument 1 to "foo" has incompatible type "**dict[str, object]"; expected "P"
+args: list[object]
+foo(*args)  # E: Argument 1 to "foo" has incompatible type "*list[object]"; expected "P"
+kwargs: dict[str, object]
+foo(**kwargs)  # E: Argument 1 to "foo" has incompatible type "**dict[str, object]"; expected "P"
 [builtins fixtures/dict.pyi]