test-clone-uncompressed: use config to silence the lock warning

The ui.timeout.warn option can solve the issue6237 in a cleaner way than what
was done in 752da6863e39. That way, possible other unexpected error output will
not be silenced.

Differential Revision: https://phab.mercurial-scm.org/D8726

tests/test-clone-uncompressed.t

@@ -407,7 +407,7 b' actually serving file content'
   $ sleep 1
   $ echo >> repo/f1
   $ echo >> repo/f2
-  $ hg -R repo ci -m "1" 2>/dev/null
+  $ hg -R repo ci -m "1" --config ui.timeout.warn=-1
   $ wait
   $ hg -R clone id
   000000000000