conformance: make TypeVarTuple test not depend on TypeVar inference behavior (#2234)

Author: JelleZijlstra

conformance/results/ty/generics_typevartuple_concat.toml

@@ -1,8 +1,8 @@
 conformance_automated = "Fail"
 conformant = "Unsupported"
 errors_diff = """
-Line 52: Unexpected errors ['generics_typevartuple_concat.py:52:1: error[type-assertion-failure] Type `tuple[@Todo(TypeVarTuple), ...]` does not match asserted type `tuple[int, bool, str]`']
+Line 53: Unexpected errors ['generics_typevartuple_concat.py:53:5: error[type-assertion-failure] Type `tuple[@Todo(TypeVarTuple), ...]` does not match asserted type `tuple[int, bool, str]`']
 """
 output = """
-generics_typevartuple_concat.py:52:1: error[type-assertion-failure] Type `tuple[@Todo(TypeVarTuple), ...]` does not match asserted type `tuple[int, bool, str]`
+generics_typevartuple_concat.py:53:5: error[type-assertion-failure] Type `tuple[@Todo(TypeVarTuple), ...]` does not match asserted type `tuple[int, bool, str]`
 """

conformance/tests/generics_typevartuple_concat.py

@@ -48,8 +48,9 @@ def prefix_tuple(x: T, y: tuple[*Ts]) -> tuple[T, *Ts]:
     raise NotImplementedError
 
 
-z = prefix_tuple(x=0, y=(True, "a"))
-assert_type(z, tuple[int, bool, str])
+def call_prefix_tuple(x: int, y: bool, z: str):
+    result = prefix_tuple(x=x, y=(y, z))
+    assert_type(result, tuple[int, bool, str])
 
 
 def move_first_element_to_last(tup: tuple[T, *Ts]) -> tuple[*Ts, T]: