MPP-3730: Fix login redirects in dev/stage/prod

[rafeerahman]

Closing this PR. find_file_at_path does not return None.

This PR fixes MPP-3730.

Bug description

These URLs works, redirects to the API profile page after login:

https://dev.fxprivaterelay.nonprod.cloudops.mozgcp.net/accounts/fxa/login/?next=/api/v1/profiles/

https://stage.fxprivaterelay.nonprod.cloudops.mozgcp.net/accounts/fxa/login/?next=/api/v1/profiles/

https://relay.firefox.com/accounts/fxa/login/?next=/api/v1/profiles/

Locally, accounts/fxa/login/?next=/faq/ works. It does not work in stage/dev/prod because we use staticfiles, redirects to the dashboard instead of the FAQ and emits a Sentry error:

https://dev.fxprivaterelay.nonprod.cloudops.mozgcp.net/accounts/fxa/login/?next=/faq/

https://stage.fxprivaterelay.nonprod.cloudops.mozgcp.net/accounts/fxa/login/?next=/faq/

https://relay.firefox.com/accounts/fxa/login/?next=/faq/

Sentry Issue: RELAY-JH

Screenshot (if applicable)

How to test

1. push to dev server and go to https://dev.fxprivaterelay.nonprod.cloudops.mozgcp.net/accounts/fxa/login/?next=/faq/

2. Verify you are redirected to the faq page.

Checklist (Definition of Done)

• [ ] Product Owner accepted the User Story (demo of functionality completed) or waived the privilege.
• [ ] Customer Experience team has seen or waived a demo of functionality.
• [ ] All acceptance criteria are met.
• [ ] Jira ticket has been updated (if needed) to match changes made during the development process.
• [ ] I've added or updated relevant docs in the docs/ directory
• [ ] Jira ticket has been updated (if needed) with suggestions for QA when this PR is deployed to stage.
• [ ] All UI revisions follow the coding standards, and use Protocol tokens where applicable (see /frontend/src/styles/tokens.scss).
• [ ] Commits in this PR are minimal and have descriptive commit messages.
• [ ] l10n changes have been submitted to the l10n repository, if any.

[sentry-io[bot]]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: privaterelay/allauth.py

Function	Unhandled Issue
is_safe_url	AttributeError: 'NoneType' object has no attribute 'get_response' /ac... Event Count: 3

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