fix: skip bootstrapping-infra job for fork PRs

[Copilot]

Fork PRs don't receive repository secrets, causing azure/login@v1 to fail with "Not all values are present" when OIDC_AZURE_CLIENT_ID/OIDC_AZURE_TENANT_ID resolve to empty strings.

Change

Added a job-level if condition to .github/workflows/bootstrapping-infra.yml:

jobs:
  build:
    if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository

• workflow_dispatch / schedule: unaffected, always runs
• PRs from the same repo: unaffected, still runs
• PRs from forks: job is skipped — no credentials available, infrastructure bootstrapping cannot proceed anyway