Codejail remote_exec fails to serialize bytes

[timmc-edx]

send_safe_exec_request_v0 in edxapp's remote_exec.py is raising builtins.TypeError: Object of type bytes is not JSON serializable in some cases when attempting to serialize data for the codejail API. (Just a handful in the past few days). This occurs in the statement payload = json.dumps(data).

Likely this is a preexisting issue with the codejail api client, but we should investigate. (We probably need to call codejail's json_safe function—or find out what's passing in bytes objects.)

Acceptance criteria:

• Stop seeing logs matching env:prod service:edx-edxapp-lms "safe_exec.py" "TypeError: Object of type bytes is not JSON serializable"

[timmc-edx]

This should fix it: openedx/edx-platform#36542

[timmc-edx]

Haven't seen this reoccur since April 15 (8 days ago). There were only a handful that week, but none this week. I think we can call this good.