chore: skip form action tests on webkit build

[dummdidumm]

fetch requests sometimes for unknown reasons go into the abyss and never fire off, most commonly on webkit during build mode - therefore disable tests there

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[benmccann]

I think I'd lean towards opt-in rather than opt-out for the webkit tests. There's a few PRs dealing with this, so I opened an issue so that we can have a single place to discuss: #8578 (or now we have four places instead of three 😆)

[benmccann]

Closing this since #8585 was merged