BUG: fix two bugs with symlog colorbar ticks for matplotlib 3.5

[neutrinoceros]

PR Summary

fix #3554
fix #3560

[neutrinoceros]

Ah, this is one more place we need versioned branches to support various versions of MPL apparently

[neutrinoceros]

switching to draft while we're stabilizing the auto backporting system

[cphyc]

Could you document why this fixes the issue?

[neutrinoceros]

actually it's pretty hard to follow matplotlib's dev. I know they've been doing drastic refactors to the colobar objects, and I could point to the exact PRs where that happened, but their line changes are very large (+1k/-1k typically).
My guess is that this "offset" is actually an off-by-one error that slipped into yt because it was compensated by an equivalent mistake in matplotlib, which is why we need to keep it for versions older than 3.5, hence this bizarre construct. Anyway I tried to just remove this offset completely but unfortunately it broke for Matplotlib 3.4
Should I use some of this comment and bundle it with the code ?

[neutrinoceros]

@cphyc it seems you enabled auto-merging here but didn't formally approve (which is required for auto-merge).

[neutrinoceros]

@meeseeksdev backport to yt-4.0.x

[lumberbot-app]

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 yt-4.0.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 82eee9c409756f9d157573530d3438cc8da124bc

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

$ git commit -am 'Backport PR #3556: BUG: fix two bugs with symlog colorbar ticks for matplotlib 3.5'

4. Push to a named branch :

git push YOURFORK yt-4.0.x:auto-backport-of-pr-3556-on-yt-4.0.x

5. Create a PR against branch yt-4.0.x, I would have named this PR:

"Backport PR #3556 on branch yt-4.0.x (BUG: fix two bugs with symlog colorbar ticks for matplotlib 3.5)"

And apply the correct labels and milestones.

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

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

If these instruction are inaccurate, feel free to suggest an improvement.