Update standards version to 4.7.3, no changes needed.

Upgrade checklist verified:
 4.6.2 → 4.7.0:
  * Package does not use dpkg-divert
 4.7.0 → 4.7.1:
  * Package does not install to non-/usr paths
Certainty: certain
Fixed-Lintian-Issues:
 source: ancient-standards-version 4.6.2 (released 2022-12-17) (current is 4.7.3.0)
