ext,tests: Update the testlib download URL for v21.2

Change-Id: I36bb8208485536482f30ef77f6e509379481b5ee
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/54467
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed