ci: run stale workflow once daily (cron */10 fires every 10 minutes)

[kobihikri]

Hi, and thank you for Zuul.

One-character CI fix: stale.yml's schedule is

- cron: "*/10 5 * * *"

*/10 in the minutes field means every 10 minutes during hour 05 UTC — up to 6 runs a day for a job that only needs one (the run history shows the repeats, e.g. 05:45 and 06:32 today). It looks like a typo for the common "once daily at 05:10":

- cron: "10 5 * * *"

That's the whole change — same behavior, 6× fewer runner minutes and API calls.

For transparency: I used AI assistance to spot and draft this; I verified the cron line and the duplicate run history myself.