CI: Process stale issues twice per day

[hugovk]

This action starts with the first issue, then moves on to the next. Once it's processed a batch, it saves its progress in a small cache file.

As detailed in #113858, the rest of the CI generates lots of large cache files, which means the (small) actions/stale cache file has been cleared out by the time the next daily cron triggers.

This means the action starts again at the top, and reprocesses the same batch over and over, never making progress.

Let's try running twice a day. This should hopefully keep the "last access" of the cache file fresher, meaning it's not cleared out. We could later also try 3 or 4 times per day.

[hugovk]

Let's try running twice a day. This should hopefully keep the "last access" of the cache file fresher, meaning it's not cleared out. We could later also try 3 or 4 times per day.

Twice a day is not enough:

The saved state was not found, the process starts from the first issue.

• https://github.com/python/cpython/actions/runs/8257386961/job/22587844299#step:2:24
• https://github.com/python/cpython/actions/runs/8264321477/job/22607678470#step:2:24
• https://github.com/python/cpython/actions/runs/8273399574/job/22637098149#step:2:24
• https://github.com/python/cpython/actions/runs/8280384019/job/22656774950#step:2:24
• https://github.com/python/cpython/actions/runs/8289314116/job/22685512167#step:2:24

Let's try 4x: #116857