Add the ruby version to the current release (heroku#1555)

* Add the ruby version to the current release

This task runs after the new version is injected into the CHANGELOG. That means that if we add something under "unreleased" at this point, then it shows up in the wrong section. This commit fixes it.

* Remove extra trailing newline

Author: schneems

.github/workflows/document_ruby_version.yml

@@ -24,11 +24,11 @@ jobs:
     with:
       custom_update_command: |
         set -euo pipefail
+        DATE_TODAY="$(date --utc --iso-8601)"
 
-        sed --in-place '/## \[Unreleased\]/a\
-        \
-        - ${{ inputs.is_jruby && 'J' || ''}}Ruby ${{inputs.ruby_version}} is now available
-        ' CHANGELOG.md
+        sed --in-place "/## \[v${NEW_VERSION}\] - ${DATE_TODAY}/a\\
+        \\
+        - ${{ inputs.is_jruby && 'J' || ''}}Ruby ${{inputs.ruby_version}} is now available" CHANGELOG.md
 
         sed --in-place --regexp-extended \
           --expression "s/v${EXISTING_VERSION}/v${NEW_VERSION}/" \