⬆️ Bump actions/github-script from 8 to 9

[AnandChowdhary]

Summary

• updates all five PR Generator CI steps to actions/github-script@v9
• keeps the current script API usage intact; none imports or redeclares the v9-injected getOctokit
• replaces stale Dependabot PR ⬆️ Bump actions/github-script from 8 to 9 #160 from current master

Validation

• Node 12.22.12 / npm 6.14.16: npm ci, npm run build, and npm test (2 suites, 2 tests)
• Parsed the workflow YAML; actionlint passed; compiled all five github-script blocks against the v9 injected context
• git diff --check and added-line security scan passed
• Independent Codex review: passed with no security or logic findings

Supersedes #160.