CI/WEB: Fix github quota errors by using website as cache
xref #50485

Looks like the previous approach didn't fix the github quota errors. @mroeschke I saw you also added a github token, but that didn't seem to work either.

What I'm doing here is to save the data we fetch from github in the website. For example https://pandas.pydata.org/maintainers.json (also for releases and pdeps). The, we request data from github normally, but if the quota is exceeded, if fallbacks to that json file with the data of the previous build. In the worst case scenario we'll have some delay updating the info in the website (we use the quota on PRs, and it can happen that for commits to main that update the cache files, we don't have quota for a while). But we shouldn't see any other CI failure caused by the github quota.

Since building the website shouldn't fail anymore, in the CI or locally, I remove the `--ignore-io-errors` parameter of the script, which doesn't make sense anymore. Also the previous cache, and the token, which I think they didn't help much.

I also found a typo when fetching the PDEPs under discussion, that was preventing to render then in the roadmap page. It's also being fixed here.
@phofl @MarcoGorelli do you want to have a look at this before I merge? CI error is because a pytest worker didn't return, but the tests passed there.

Would be good to get this merged before the release, so the quota error doesn't happen when publishing the prod docs, and we can forget about the error later too. Thanks for having a look. I'll merge, and if there is any problem I'll address in a follow up. But I tested it quite well, should work. Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

```
git checkout 1.5.x
git pull
```

2. Cherry pick the first parent branch of the this PR on top of the older branch:
```
git cherry-pick -x -m1 afdf0a3e409d02cdfff6c813f512717f1503a4d8
```

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

```
git commit -am 'Backport PR #50811: CI/WEB: Fix github quota errors by using website as cache'
```

4. Push to a named branch:

```
git push YOURFORK 1.5.x:auto-backport-of-pr-50811-on-1.5.x
```

5. Create a PR against branch 1.5.x, I would have named this PR:

> "Backport PR #50811 on branch 1.5.x (CI/WEB: Fix github quota errors by using website as cache)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the `Still Needs Manual Backport` label once the PR gets merged.

If these instructions are inaccurate, feel free to [suggest an improvement](https://github.com/MeeseeksBox/MeeseeksDev).
                