Bug 1828556 [wpt PR 39589] - Reset the popover invoker in `showPopove…

…r()`, a=testonly

Automatic update from web-platform-tests
Reset the popover invoker in `showPopover()`

As was pointed out in [1], if we don't reset invoker, it is possible
to get into a state where a closed popover still has an invoker. The
new test case in this CL shows that problem.

[1] whatwg/html#9152

Bug: 1307772
Change-Id: I1511ec8f0e9e0193f0c8b5ce834d20de9d8b46e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4435697
Reviewed-by: Joey Arhar <jarharchromium.org>
Commit-Queue: Tommy Steimel <steimelchromium.org>
Code-Coverage: Findit <findit-for-meappspot.gserviceaccount.com>
Auto-Submit: Mason Freed <masonfchromium.org>
Reviewed-by: Tommy Steimel <steimelchromium.org>
Cr-Commit-Position: refs/heads/main{#1133290}

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wpt-commits: cc0704e3a1741d28d2bef73c6e84796b7c928849
wpt-pr: 39589

UltraBlame original commit: cea57aad3268804342d5b82c3ae3a22d51ac1e8a