replace: mark unused parameter in ref callback

replace: mark unused parameter in ref callback

We don't look at the "flags" parameter, which is natural for something
that is just printing the contents of the replace refs. But let's mark
it to appease -Wunused-parameter.

This probably should have been part of 63e14ee2d6 (refs: mark unused
each_ref_fn parameters, 2022-08-19), but I missed it as this one is a
repo_each_ref_fn, which takes an extra repository argument.

Signed-off-by: Jeff King <redacted>
Signed-off-by: Junio C Hamano <redacted>