ci: prevent duplicate runs on PRs, add Java 25 to matrix

[Copilot]

CI was triggering twice for pull requests — once for the push event on the PR branch and once for the pull_request event.

Changes

• Scoped push trigger to master only — PR branches now only trigger CI via pull_request, eliminating the duplicate run
• Added Java 25 to the build matrix: [8, 11, 21, 25]

on:
  push:
    branches:
      - master
  pull_request:

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Trigger CI on the repository's default branch

Limiting push to master means this workflow will not run for pushes/merges on repositories whose active branch is main (which is the branch present in this repo), so post-merge CI and any direct-push validation are silently skipped. This change prevents duplicate PR runs, but in a main-based repo it also removes the only push-event coverage for the default branch.

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