[wing328]

to close #24697
to close #24696

PR checklist

• Read the contribution guidelines.
• 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.
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

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Summary by cubic

Unifies the Apache HttpClient version used by the Java apache-httpclient generator to 5.6.3 to pick up upstream fixes and align Gradle and Maven outputs. Previously Gradle templates/samples used 5.1.3 and Maven used 5.2.1; now both use 5.6.3.

• Updates httpclient_version in build.gradle.mustache and <httpclient-version> in pom.mustache; regenerates affected samples.
• No generator logic changes; only dependency version bump. Generated clients will now reference org.apache.httpcomponents.client5:httpclient5 5.6.3.
• Migration: Regenerate Java clients to adopt 5.6.3. If you pin the dependency in your project, no action is required.

^{Written for commit 2155e00. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 8 files

_{Re-trigger cubic}