Bump baseline to Java 21

[uhafner]

Official Java 17 support ends soon. So it also makes sense to make use of modern Java API. And Jenkins is moving to Java 2 soon, so we will not break anything.

[github-actions]

☀️   Quality Monitor

Tests

     Unit Tests (Whole Project): 100.00% successful (86 passed, 2 skipped)
   ⛔   Architecture Tests (Whole Project): 100.00% successful (17 passed, 2 skipped)

Coverage for New Code

   〰️   Line Coverage (Changed Code): 100.00% (0 missed lines)
   ➰   Branch Coverage (Changed Code): n/a (0 missed branches)
     Mutation Coverage (Changed Code): n/a (0 survived mutations)
   💪   Test Strength (Changed Code): n/a (0 survived mutations in tested code)

Coverage for Whole Project

   〰️   Line Coverage (Whole Project): 91.22% (64 missed lines)
   ➰   Branch Coverage (Whole Project): 90.45% (21 missed branches)
     Mutation Coverage (Whole Project): 84.38% (60 survived mutations)
   💪   Test Strength (Whole Project): 89.26% (39 survived mutations in tested code)

Style

     CheckStyle (Whole Project): No warnings
     PMD (Whole Project): No warnings
   ☕   Java Compiler (Whole Project): No warnings

Bugs

     SpotBugs (Whole Project): No bugs
   🐛   Error Prone (Whole Project): No bugs

API Problems

   🚫   Revapi (Whole Project): 1 warning (high: 1)

Vulnerabilities

   🛡️   OWASP Dependency Check (Whole Project): No vulnerabilities

Software Metrics

   🌀   Cyclomatic Complexity (Whole Project): 377 (total)
   💭   Cognitive Complexity (Whole Project): 174 (total)
   ➿   N-Path Complexity (Whole Project): 341 (total)
   📏   Lines of Code (Whole Project): 4282 (total)
   📝   Non Commenting Source Statements (Whole Project): 1261 (total)
   🔗   Class Cohesion (Whole Project): 71.43% (maximum)
   ⚖️   Weight of Class (Whole Project): 100.00% (maximum)

🚦 Quality Gates

Overall Status: ✅ SUCCESS

✅ Passed Gates

• ✅ Overall Tests Success Rate: 100.00 >= 100.00
• ✅ Line Coverage in New Code: 100.00 >= 90.00
• ✅ Branch Coverage in New Code: 100.00 >= 90.00
• ✅ Mutation Coverage in New Code: 100.00 >= 90.00
• ✅ Potential Bugs in Whole Project: 0.00 <= 0.00
• ✅ Style Violation in Whole Project: 0.00 <= 0.00

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Created by Quality Monitor v4.0.0-rc2 (#615f6ae). More details are shown in the GitHub Checks Result.