Tests: Disable a whitespace-setting test in Edge 14

Tests: Disable a whitespace-setting test in Edge 14

Working around this problem would require us to skip setting whitespace-only
values except when they're valid which would be very fragile. Another option
would be to set the value and see if it succeeded and then react to that.

We've tried something like that in the past to be able to overwrite !important
styles (see 24e5879) but it broke the CSS cascade (see
https://bugs.jquery.com/ticket/14836#comment:5) and was triggering
MutationObserver callbacks too often so it was reverted in PR gh-1532.

Ref gh-3204
Ref gh-1532