BCDA-7437: Update sandbox credentials

[kyeah]

🎫 Ticket

https://jira.cms.gov/browse/BCDA-7437

🛠 Changes

• Rotate sandbox credentials to ensure continuity of testing

ℹ️ Context for reviewers

This rotates our documented shared sandbox credentials so folks can continue to use our sandbox environment :)

✅ Acceptance Validation

Verified each credential individually against our /token endpoint.

🔒 Security Implications

• This PR adds a new software dependency or dependencies.
• This PR modifies or invalidates one or more of our security controls.
• This PR stores or transmits data that was not stored or transmitted before.
• This PR requires additional review of its security implications for other reasons.

[alex-dzeda]

Looks good, confirmed the last one works + you smoke tested others.