[WebGPU] unpack4x8unorm does not appear to be implemented
<rdar://problem/120107356>
Duplicate of bug 266870?
*** Bug 266870 has been marked as a duplicate of this bug. ***
Pull request: https://github.com/WebKit/WebKit/pull/22262
Committed 272528@main (41341242c718): <https://commits.webkit.org/272528@main> Reviewed commits have been landed. Closing PR #22262 and removing active labels.