Update java undertow to newer version

[wing328]

to close #22758

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• File the PR against the correct branch: master (upcoming 7.x.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR solves a reported issue, reference it using GitHub's linking syntax (e.g., having "fixes #123" present in the PR description)
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Summary by cubic

Upgrade Undertow to 2.3.21.Final for the Java Undertow server generator and sample to pick up the latest fixes. No generator logic changes.

• Dependencies
  • Update version in modules/openapi-generator/src/main/resources/java-undertow-server/pom.mustache.
  • Update version in samples/server/petstore/java-undertow/pom.xml.

^{Written for commit 76b0bac. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files