fix(jjwt-jackson): update test API usage and jvmArgs for 0.12.0 metadata

[erguiti-imane]

fix: add reachability metadata for jjwt-jackson 0.12.0

• Updated test usage to Jwts.parser() instead of parserBuilder() to align with jjwt-jackson 0.12.0 API.
• Ensures native-image-agent can generate metadata without crashing due to illegal reflective access.
• Added required JVM arguments to the test task to allow reflective access to internal JDK classes:
  • --add-opens=java.base/sun.security.util=ALL-UNNAMED
  • --add-opens=java.base/java.io=ALL-UNNAMED
• Generated reflect-config.json is now valid for jjwt-jackson 0.12.0.

What does this PR do?

Code sections where the PR accesses files, network, docker or some external service

• (example link to code section)

Checklist before merging

• I have considered including reachability metadata directly in the library or the framework (see our contributing document)
• I am the original author of all content provided in the pull request, and I did not copy the content from any other source (see the tests section from our contributing document)
• For all tests where I am not the sole author, I have added a comment that proves I may publish them under the specified license (see the tests section from our contributing document)
• I have properly formatted metadata files (see our formatting guide)
• I have added thorough tests (see the tests section from our contributing document)
• I have filled all places where my pull request accesses files, network, docker, or any other external service (see the section above)