Fix and update link-check

[rogermparent]

Context: #2932

This PR fixes the odd failures that are happening on PRs by using fetch-depth: 0 on the checkout action, allowing full access to all branches' git history and allowing so we can do a proper github-like diff that doesn't include origin/master changes that have happened since the PR in question.

Separately, this PR upgrades link-check to a new version that uses a small change that uses a single command of git diff origin/master...HEAD instead of a two-step merge-base and diff. Functionally the same thing (probably didn't need a minor bump, just a patch, but oh well we're still in 0.x.x), just more simple and elegant- the only reason we didn't do it before is I wasn't aware of triple-dot syntax. I tested this new version a couple times to make sure it doesn't just break everything, and it works fine.

One big caveat is that merging master (or any Gatsby 3 commit) into our current Gatsby 2 PRs that currently have this issue will cause caching havoc that needs manual intervention to be remedied. I can do so for PRs that really need it, but I'd suggest using local link-check instead since everyone probably has full commit history locally and it should work. At least we'll have it solved for the future!

[rogermparent]

Tested on #2932, this fixes the link-check problem because origin/master was inaccessible without it under some circumstances and accessible in others. I don't know the exact circumstances because cloud is a nightmare to debug- maybe it just had to be multiple commits in and then the shallow copy cut it off?

[rogermparent]

Next update I should sync up the action version tag and the NPM version, this can get a little confusing.

[rogermparent]

This just applies to the local CLI script.

[jorgeorpinel]

Thanks @rogermparent ! Looks good i.e. I'd approve but

merging master (or any Gatsby 3 commit) into our current Gatsby 2 PRs that currently have this issue will cause caching havoc that needs manual intervention to be remedied

That sounds scary haha. No matter when we merge this there will be several PRs open that may require merging master to solve conflicts. Are you suggesting we just ignore the CI link-checker for those?

[rogermparent]

Are you suggesting we just ignore the CI link-checker for those?

I was thinking of that on the CI level, but maybe we can get a decent mid-ground fix by just cherry-picking this commit into the PRs that need it, especially since only one line is actually needed to patch the problem. I can look into that today.

[rogermparent]

Just did a retroactive update on the existing PRs that have the problem- without a full master merge, they don't require manual intervention and we get CI results from link-check!

git checkout link-check-checkout-deep .github/workflows/link-check-deploy.yml && git commit -am "Fix link-check" && git push have been run on all the PRs that I saw having an issue. There's probably others that just happen not to be having an issue right now, in which case the same command can be run with no other intervention needed.

Beyond that, once this is merged we shouldn't run into the same issue in the future.

[julieg18]

Looks good!