Fix post_bulk annual limit validation

[whabanks]

Summary | Résumé

This PR fixes incorrect annual limit validation when posting bulk emails via the API. We were counting SMS + Email notifications when validating if a job would put the service over their Email annual limit.

Related Issues | Cartes liées

Test instructions | Instructions pour tester la modification

1. Set email and sms annual limits to 10
2. Send 5 SMS messages
3. Send 5 Email messages
4. Via the API create a bulk email send of 4
5. Verify it succeeds and does not result in error messages containing negative annual limit counts.

Release Instructions | Instructions pour le déploiement

None.

Reviewer checklist | Liste de vérification du réviseur

• This PR does not break existing functionality.
• This PR does not violate GCNotify's privacy policies.
• This PR does not raise new security concerns. Refer to our GC Notify Risk Register document on our Google drive.
• This PR does not significantly alter performance.
• Additional required documentation resulting of these changes is covered (such as the README, setup instructions, a related ADR or the technical documentation).

⚠ If boxes cannot be checked off before merging the PR, they should be moved to the "Release Instructions" section with appropriate steps required to verify before release. For example, changes to celery code may require tests on staging to verify that performance has not been affected.