t1800: loosen matching of error message for bad shebang

t1800: loosen matching of error message for bad shebang

t1800.16 checks whether an attempt to run a hook script with a missing
executable in its #! line fails and reports that error.  The expected
error message differs between platforms.  The test handles two common
variants, but on NonStop OS we get a third one: "fatal: cannot exec
'bad-hooks/test-hook': ...", which causes the test to fail there.

We don't really care about the specific message text all that much here.
Use grep and a single regex with alternations to ascertain that we get
an error message (fatal or otherwise) about the failed invocation of the
hook, but don't bother checking if we get the right variant for the
platform the test is running on or whether quoting is done.  This looser
check let's the test pass on NonStop OS.

Reported-by: Randall S. Becker <randall.becker@nexbridge.ca>
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>