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
1 file changed