Fail the version sync when it matches nothing

replaceregexp reports nothing when it matches nothing, so a renamed or dropped
axis2.version property would leave a userguide sample pinned to a stale version
and the release would carry on quietly -- the failure mode the sync exists to
prevent. Count the poms, count the ones carrying the version being released, and
fail on a mismatch naming the counts.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>