The error message when destroying a held snapshot no longer is `dataset
is busy` but `it's being held. Run 'zfs holds -r <snapshot>' to see
holders.`
The existing `destroySnapshotsErrorRegexp` parses both formats
correctly, but downstream test assertions in platformtest were checking
for the literal `dataset is busy` string.
refs
- the PR that adds ZFS 2.3 & 2.4 to CI:
https://github.com/zrepl/zrepl/pull/921
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>