Commit faa0ee9844 accidentally broke the way split snapshot mutation was
frozen -- instead of appending the sub-mutation `m` the commit kept the
old variable name of `mut` which in the new code corresponds to "old"
non-split mutation
Fixes#29051
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Closesscylladb/scylladb#29052