tests/9p: add missing Rgetattr response name

tests/9p: add missing Rgetattr response name

'Tgetattr' 9p request and its 'Rgetattr' response types are already used
by test client, however this response type is yet missing in function
rmessage_name(), so add it.

Fixes: a6821b828404 ("tests/9pfs: compare QIDs in fs_walk_none() test")
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <e183da80d390cfd7d55bdbce92f0ff6e3e5cdced.1732465720.git.qemu_oss@crudebyte.com>
(cherry picked from commit 4ec984965079b51a9afce339af75edea6de973a2)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>