Prepare release v81

[heroku-linguist]

Commits since the last release:

• Improve detection error message with better user experience (Improve detection error message with better user experience #270)
• Bump the ruby-dependencies group with 2 updates (Bump the ruby-dependencies group with 2 updates #272)
• Improve openjdk::install_openjdk_via_jvm_common_buildpack (Improve OpenJDK installation via jvm-common buildpack #275)
• Fix trailing whitespace in output functions (Fix trailing whitespace in output functions #274)
• Bump the ruby-dependencies group with 2 updates (Bump the ruby-dependencies group with 2 updates #276)
• Improve CHANGELOG formatting (Improve CHANGELOG formatting #279)
• Bump rubocop-rspec from 3.7.0 to 3.8.0 in the ruby-dependencies group (Bump rubocop-rspec from 3.7.0 to 3.8.0 in the ruby-dependencies group #277)
• Bump actions/checkout from 5 to 6 (Bump actions/checkout from 5 to 6 #278)
• Improve README structure and documentation (Improve README structure and documentation #281)
• Use buildpack banner from heroku/buildpacks (Use buildpack banner from heroku/buildpacks #280)
• Bump rubocop from 1.81.7 to 1.82.1 in the ruby-dependencies group (Bump rubocop from 1.81.7 to 1.82.1 in the ruby-dependencies group #282)
• Bump the ruby-dependencies group with 2 updates (Bump the ruby-dependencies group with 2 updates #283)
• Switch to AWS' dual-stack S3 URLs (Switch to AWS' dual-stack S3 URLs #284)

For the full diff, see the compare view:
v80...main