tests: also test spaces in conflict marker labels
Our fake merge tool printed the arguments using `$1` etc. without
quotes, which means that the shell collapsed repeated spaces within
the argument. That resulted in tests that did not pick up changes to
the number of spaces.
Differential Revision: https://phab.mercurial-scm.org/D12010
$ LANG=nonexistent LC_ALL=nonexistent LANGUAGE=nonexistent hg version -q
Mercurial Distributed SCM (version *) (glob)