Release 0.72.1 #6030

Target release date is the end of September 2026

Post release tasks:

• merge Remove uri package from website ponylang-website#1439
• merge Update README for stdlib move uri#59
• archive ponylang/uri
• merge Update README for stdlib move courier#98
• archive ponylang/courier
• ponylang/stallion: switch pr.yml and pony-lint.yml container images from :nightly back to :release
• ponylang/github_rest_api: switch pr.yml and pony-lint.yml container images from :nightly back to :release
• ponylang/ponyup: switch pr.yml container image from :nightly back to :release, macOS install script from nightly back to release, Windows cloudsmith URLs from nightlies back to releases; switch pony-lint.yml container image from :nightly back to :release