Do not fail for external PRs

[abitrolly]

Sourcegraph CI/CD failures on PR generate emails that distract from actual problems.

I can add the rule to skip the job if the action is not from the same repo like in https://github.com/sourcegraph/sourcegraph/pull/43783 but maybe it is possible to use standard token.

GITHUB_TOKEN: ${{ secrets.CODENOTIFY_GITHUB_TOKEN || secrets.GITHUB_TOKEN }}