TST: skip if known-bad version of imagemagick

[tacaswell]

PR Summary

xref ImageMagick/ImageMagick#2720

This should un-break OSX on azure and travis, prevent breakage on other CI as the imagemagick update makes its way through packaging.

[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 v3.3.x
$ git pull

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

$ git cherry-pick -m1 d1a9b21ba389d4328263e9a5415d630330605cdf

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

$ git commit -am 'Backport PR #18730: TST: skip if known-bad version of imagemagick'

4. Push to a named branch :

git push YOURFORK v3.3.x:auto-backport-of-pr-18730-on-v3.3.x

5. Create a PR against branch v3.3.x, I would have named this PR:

"Backport PR #18730 on branch v3.3.x"

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!

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

[tacaswell]

This test is not on the 3.3.x branch (came in via 9cee283 #18501) so no need to backport.