t/t-migrate-info.sh: improve option error tests
t/t-migrate-info.sh: improve option error tests

We refactor the tests of various invalid options to the
"git lfs migrate info" command to use the same checks as
those found in the t/t-migrate-fixup.sh tests, among others.
This allows us to confirm both the error message text and
that the command fails as expected.

github/git-lfs,github/git-lfs,github/git-lfs