test(apicompat): avoid unchecked tool history assertions

backend/internal/pkg/apicompat/responses_client_tools_test.go

@@ -133,7 +133,9 @@ func TestAdaptResponsesClientToolsWithInheritedMapping_ExplicitToolsReplaceInher
 	require.NoError(t, err)
 	require.False(t, changed)
 	require.Empty(t, mapping)
-	require.Equal(t, "custom_tool_call", req["input"].([]any)[0].(map[string]any)["type"])
+	items := requireResponsesClientToolValue[[]any](t, req["input"])
+	call := requireResponsesClientToolValue[map[string]any](t, items[0])
+	require.Equal(t, "custom_tool_call", call["type"])
 }
 
 func TestRestoreResponsesClientToolPayload_RestoresClientAndNamespaceCalls(t *testing.T) {