Emails - Staging - links are redirect to production instead of staging

Pre condition - approved funds allocation proposal on Staging
Steps to reproduce:

1. get email that your proposal is approved "[TEST] Funding proposal was approved"
2. Click on the common id link.

Actual results:
user redirect to production and get 404 error

Expected results:
user must redirect to the common on staging

No file or test is named. Start by tracing how the staging email for an approved funding proposal builds its common ID link, then compare the target host with the staging host. Reproduce the email flow described in the issue and verify that clicking the link opens the common on staging rather than production and avoids the 404.

Written by the indexing model from the issue text.