[fix][ci] Skip pull request title check outside apache/pulsar

[lhotari]

Motivation

The semantic pull request title check also runs in forks, where pull requests used for personal CI or development may not follow Apache Pulsar's title convention.

Modifications

Run the title-check job only when github.repository == 'apache/pulsar'. Pull requests in other repositories skip the job, while pull requests targeting apache/pulsar continue to be checked, including those submitted from forks.

Verifying this change

This is a workflow-only change without added test coverage. Local validation passed:

• actionlint .github/workflows/ci-semantic-pull-request.yml
• git diff --check
• ./gradlew spotlessCheck checkstyleMain checkstyleTest

Does this pull request potentially affect one of the following parts:

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment