build: use Java 21

[jnodorp-jaconi]

Pull request checklist

Pull request structure

• Make sure you are requesting to pull a topic/feature/bugfix branch (right side). Don't request your main!
• Make sure you are making a pull request against the main branch (left side). Also you should start your branch off our main.
• Check the commits message styles matches our requested structure.

Implementation checks

• Tests for the changes have been added.
• Docs have been reviewed and added / updated if needed.
• Tests (gradle clean check) have passed locally any fixes were made for failures.
• GitHub checks all pass (GH Actions, Sonar, Codecov).

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

Does this introduce a breaking change?

• Yes
• No

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.21%. Comparing base (0f28b01) to head (002fe50).

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #255   +/-   ##
=========================================
  Coverage     86.21%   86.21%           
  Complexity      123      123           
=========================================
  Files            27       27           
  Lines           312      312           
  Branches         31       31           
=========================================
  Hits            269      269           
  Misses           27       27           
  Partials         16       16           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud