[test] t/stress/rpa-splice.t: reproducible testcases for GH #766

with asan:
t/stress/rpa-splice.t (Wstat: 10752 Tests: 225 Failed: 42)
  Failed tests:  11-12, 16, 36-37, 41, 61-62, 66, 81-82
                86-87, 91, 106-107, 111-112, 116, 131-132
                136-137, 141, 151-152, 156, 161-162, 166
                176-177, 181, 186-187, 191, 201-202, 206
                211-212, 216