Add GIN to linkcheck ignore list

[alessandrofelder]

Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?

GIN being down seems to be the root cause of build errors, including on main, and leading to a mismatch between the code on main and brainglobe.info.

We will still be notified of GIN being down via our scheduled (e.g. Atlas API) tests.

What does this PR do?

Adds GIN's URL to ignore-list for link checker.

References

Closes #494

How has this PR been tested?

Keeping this PR in draft until CI passes.
I will continue to check in on the build and triple-check but hard to test locally.

Is this a breaking change?

Nope.

Does this PR require an update to the documentation?

Is one.

[alessandrofelder]

uol.de was throttling us last night but seems to be fine after rerunning CI now (if that happens again, we can add it to the ignore list).

Generally, we might want to ignore/skip linkcheck errors after merging, so main and what is renders on the website are always in-sync: neuroinformatics-unit/actions#163

[adamltyson]

uol.de was throttling us last night but seems to be fine after rerunning CI now (if that happens again, we can add it to the ignore list).

I think this happens with most websites occasionally, I don't think we should just add everything to link check, otherwise we may as well not bother having it! I think the issue is just because we have so many links, and many of these are to academic sites and small blogs etc, that at any time the likelihood of >1 of them being down is pretty high.