builtin/for-each-ref: align usage string with the man page

builtin/for-each-ref: align usage string with the man page

Usage string for `git for-each-ref` was out of sync with its official
documentation. The test `t0450-txt-doc-vs-help.sh` was marked as broken
due to this.

Update the usage string to match the documentation. This allows the test
to pass, so remove the corresponding 'known breakage' marker from the
test file.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: shejialuo <shejialuo@gmail.com>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Meet Soni <meetsoni3017@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>