fix: Members not being able to test credentials with external secrets

[valya]

Summary

When a instance member opens a credential in a project with an instance owner/admin that's using external secrets, the connection test would always show as failing. This fix allows the user to test the connection, but no see the secrets themselves.

Review / Merge checklist

• [x] PR title and summary are descriptive. Remember, the title automatically goes into the changelog. Use (no-changelog) otherwise. (conventions)
• [ ] Docs updated or follow-up ticket created.
• [ ] Tests included.

  A bug is not considered fixed, unless a test is added to prevent it from happening again. A feature is not complete without tests.