Fix test source reference

If not referencing the filegroup, the package name is not detected
correctly by metalava. This seems to have led to some IntDefs being
dropped.

Test: m sdk-annotations.zip ; diff before and after (notice
      android.test appearing)
Change-Id: I8db80aca28f73a5425618e82a2d7f5bf14e7e00a

ApiDocs.bp

@@ -60,9 +60,9 @@ stubs_defaults {
     defaults: ["android-non-updatable-stubs-defaults"],
     srcs: [
         // No longer part of the stubs, but are included in the docs.
-        "test-base/src/**/*.java",
-        "test-mock/src/**/*.java",
-        "test-runner/src/**/*.java",
+        ":android-test-base-sources",
+        ":android-test-mock-sources",
+        ":android-test-runner-sources",
     ],
     libs: framework_docs_only_libs,
     create_doc_stubs: true,