v0.36.1 — fix issue-pull's stderr capture

The call sites merged stderr into the captured payload, so the helper's
retrying-anonymously warning was prepended to the JSON and jq died with
'parse error: Expected string key before ':' at line 1, column 1'. Every caller
whose authenticated read was refused -- 63 of 64 -- failed on every scheduled
run since the workflow shipped.

read_issues now also validates that the payload is a JSON array, so a mirror
returning an HTML error page or an empty body skips that platform for the run
instead of aborting the job.