Access output files thru providers in Soong tests.

The outputFiles field on ModuleBase will be removed next.

Bug: 358425833
Test: CI
Change-Id: I6d665ac13134d9278e5908f64c454366bc6bca5e
diff --git a/cc/testing.go b/cc/testing.go
index ed567af..159f86c 100644
--- a/cc/testing.go
+++ b/cc/testing.go
@@ -713,7 +713,7 @@
 func checkSnapshotIncludeExclude(t *testing.T, ctx *android.TestContext, singleton android.TestingSingleton, moduleName, snapshotFilename, subDir, variant string, include bool, fake bool) {
 	t.Helper()
 	mod := ctx.ModuleForTests(moduleName, variant)
-	outputFiles := mod.OutputFiles(t, "")
+	outputFiles := mod.OutputFiles(ctx, t, "")
 	if len(outputFiles) != 1 {
 		t.Errorf("%q must have single output\n", moduleName)
 		return