textproc/miller: Update to 5.4.0

• Remove DISTVERSIONPREFIX as upstream is no longer using it.
• Improve COMMENT.
• Add a test target.
• 5.4.0 changelog: https://github.com/johnkerl/miller/releases/tag/5.4.0

PR: 236547
Reviewed by: mat
Approved by: maintainer (timeout, >14 days)
Differential Revision: https://reviews.freebsd.org/D19593