It is convenient to use `https://api.github.com/users/$app_slug[bot]` to
obtain the corresponding account ID later.
Then build `Signed-off-by: $app_slug[bot]
<$id+$app_slug[bot]@users.noreply.github.com>`.
Currently, there is no Linux environment to build test snapshot files
GitHub's macOS runners for the past while have had some bad clock drift
which sometimes prevents this action from working with the error:
```console
'Issued at' claim ('iat') must be an Integer representing the time that the assertion was issued
```
`@octokit/auth-app` already has logic to handle this so we can defer to
that code.