The `matrix_redis_` -> `redis_` check and the `redis_` -> `valkey_`
check both stored their matches in
`matrix_playbook_migration_redis_migration_vars`.

Facts persist for the whole play, so the second check was silently
overwriting the first one's value. Nothing reads these facts outside the
block that sets them, so this was harmless in practice, but it breaks as
soon as anyone reorders the checks, reads a fact later on, or disables
one of the two checks and expects the other's value to still be around.

Name the second one after its own check, like every other check here
does.

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