test suite: gdr-subcommands: Use $peel, not $work, for a few checks

test suite: gdr-subcommands: Use $peel, not $work, for a few checks

The definition of P says
    P        result is add-patches, remaining letters apply to result~

But this was not hnoured by N n Z.  Honour it.

No change with existing tests, which do not follow P with any of
those.  But, this will be important in a moment,

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>