PYIC-7696: Update core-back to reference well-known-v4

[MikeCollingwood]

Proposed changes

What changed

• Update core-back to reference well-known-v4

Why did it change

• To contain both signing keys, allowing the rotation to happen.

Issue tracking

• PYIC-7696

Checklists

• READMEs and documentation up-to-date
• API/ unit/ contract tests have been written/ updated
• No risk of exposure: PII, credentials, etc through logs/ code
• Production changes appropriately staged out

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud