* top/maint.mk (public-submodule-commit): Remove excess quoting.
We were over-quoting the test arguments, and somewhere prior to
version 1.8.5.2.229, git stopped removing those excess quotes,
which made the test fail, since the unexpanded strings would
always differ; using GIT_TRACE=1 confirmed that the git merge-base
command wasn't even being run.
(cherry picked from commit
7a0c729aacc3716a665ce3b0c8cb34843bdecc75)