Save linkcheck cache always

[marxin]

This PR always stores the linkcheck cache when being run as part of the scheduled CI job. Note the normal PRs ignore the cache and check only the modified files. I also extended the cache expiration time so that the Nighly job can face the congressional limit from Github.com ("Server returned 429 Too Many Requests").

Hopefully, it's a viable solution.
@camelid

[Kobzol]

Sorry, due to me messing up a git operation, we sadly had to force-push the whole commit history of rustc-dev-guide :( If you'd like to update this pull request, you will have to rebase it in a special way onto the new commit history (the new master):

git fetch origin --all
git checkout <pr-branch>
git rebase --onto origin/master origin/master-old
git push --force-with-lease

More context can be found here.

[camelid]

I'm a little confused about what this change is accomplishing. Wouldn't making the cron job run every other day accomplish exactly the same thing?

[camelid]

I'm a little confused about what this change is accomplishing. Wouldn't making the cron job run every other day accomplish exactly the same thing?

Never mind, I just realized that the difference is that the cache will allow us to check new links without rechecking old links. Not sure why I didn't think of that 😅

[marxin]

Not sure why I didn't think of that 😅

Yeah, the main goal of the cache expiration is to at least partially reuse some of the GH links from the cache as one can't check all of them unless the "Server returned 429 Too Many Requests" message is hit.

[camelid]

Thanks for doing this!

[marxin]

Thanks for the fix and the CI fix you landed just after my change!