ai-policy workflow fails on fork PRs that correctly declare AI assistance

[mauro2306]

.github/workflows/ai-policy.yml fails on any pull request opened from a fork
whose commits carry an Assisted-by: trailer — that is, on exactly the
contributions that follow the AI policy.

The policy checks pass. What fails is the labelling step that runs afterwards:

- name: Label PR as AI assisted
  run: |
    gh api "repos/${{ github.repository }}/issues/${{ ... }}/labels" \
      --method POST -f "labels[]=AI assisted"

On a fork-triggered pull_request run, Actions secrets are not exposed, so
secrets.COMMAND_BOT_PAT is empty and the github.token fallback is read-only
regardless of the permissions: block. The API call returns 403 and the step
exits non-zero.

The preceding "Create 'AI assisted' label if absent" step already anticipates
this and swallows the error with || true; the labelling step does not.

Observed on nextcloud/serverinfo#1158, run log:

GITHUB_TOKEN Permissions
  Contents: read
  Issues: read
  Metadata: read
  PullRequests: read
Secret source: None
...
Found AI-assistant/Assisted-by/AI-Assisted-By trailer(s):
Assisted-by: ClaudeCode:claude-opus-5
...
gh: Resource not accessible by integration (HTTP 403)
##[error]Process completed with exit code 1.

Suggested fix

Labelling is cosmetic; the enforcement value of the workflow is in the
Signed-off-by / Co-Authored-By checks, which work fine on forks. Making the
two labelling steps non-fatal would be enough:

- name: Label PR as AI assisted
  continue-on-error: true

If the label matters on fork PRs, it needs a separate pull_request_target
workflow, since only that event grants a writable token.