Bug 1949750 [wpt PR 50860] - DOM: rename importNode()'s deep to selfOnly (and invert its value), a=testonly

Automatic update from web-platform-tests
DOM: rename importNode()'s deep to selfOnly (and invert its value)

Part of whatwg/dom#1341.

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wpt-commits: 5bcf44cb07a74e284893af96926d932ec09705e7
wpt-pr: 50860

UltraBlame original commit: 4a4c1689ebd912108057f71fa24393009d4ab18a

Author: marco-c