[External Status Checks] Replace "approved" with "passed" in API responses

Problem to solve

External Status Checks briefly used the term "approved" before we changed to use the term "passed". During that brief time, "approved" was used in the API (see "status": "approved" in documentation examples). Now we have mixed use of pending/approved and pending/pass/fail.

Proposal

Replace "approved" with "passed" in External Status Checks API responses and documentation as discussed elsewhere.