test: don't overwrite TESTDIR if already set
(cherry picked from commit 3f50fff536d715aee5e5195ec60e2af047b73c7f)
patch_name: 0105-test-don-t-overwrite-TESTDIR-if-already-set.patch
present_in_specfile: true
location_in_specfile: 105
squash_commits: true