t0033-safe-directory: check the error message without matching the trash dir

t0033-safe-directory: check the error message without matching the trash dir

Since 8959555cee (setup_git_directory(): add an owner check for the
top-level directory, 2022-03-02) when git finds itself in a repository
owned by someone else, it aborts with a "fatal: unsafe repository
(<repo path>)" error message and an advice about how to set the
'safe.directory' config variable to mark that repository as safe.
't0033-safe-directory.sh' contains tests that check that this feature
and handling said config work as intended.  To ensure that git dies
for the right reason, several of those tests check that its standard
error contains the name of that config variable, but:

  - it only appears in the advice part, not in the actual error
    message.

  - it is interpreted as a regexp by 'grep', so, because of the dot,
    it matches the name of the test script and the path of the trash
    directory as well.  Consequently, these tests could be fooled by
    any error message that would happen to include the path of the
    test repository.

Tighten these checks to look for "unsafe repository" instead.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>