py3: these two casefolding tests pass for me on my Mac

I assume the buildbot didn't catch them because it's on a
case-sensitive filesystem.

Differential Revision: https://phab.mercurial-scm.org/D5681

contrib/python3-whitelist

@@ -57,7 +57,9 b' test-bundle2-pushback.t'
 test-bundle2-remote-changegroup.t
 test-cache-abuse.t
 test-cappedreader.py
+test-casecollision-merge.t
 test-casecollision.t
+test-casefolding.t
 test-cat.t
 test-cbor.py
 test-censor.t