beforeunload-canceling.html causes the subsequent test to time out

[trflynn89]

Cancelling the beforeunload event in the Text/input/wpt-import/html/browsers/browsing-the-web/unloading-documents/beforeunload-canceling.html test seems to mess with the test infra, and causes the subsequent test to time out. For example:
https://github.com/LadybirdBrowser/ladybird/actions/runs/13138316083/job/36658995772?pr=3450

If we force headless-browser to only run this and one other test in serial, the other test will time out nearly 100% of the time:

» ./Meta/ladybird.sh run headless-browser --run-tests "${LADYBIRD_SOURCE_DIR}/Tests/LibWeb" -f beforeunload-canceling.html -f 2d.pattern.basic.nocontext.html -j1 -v
Running 2 tests...
1/2:  Start Text/input/wpt-import/html/browsers/browsing-the-web/unloading-documents/beforeunload-canceling.html
1/2: Finish Text/input/wpt-import/html/browsers/browsing-the-web/unloading-documents/beforeunload-canceling.html: 261ms
2/2:  Start Text/input/wpt-import/html/canvas/element/fill-and-stroke-styles/2d.pattern.basic.nocontext.html
2/2: Finish Text/input/wpt-import/html/canvas/element/fill-and-stroke-styles/2d.pattern.basic.nocontext.html: 30005ms
==========================================================
Pass: 1, Fail: 0, Skipped: 0, Timeout: 1, Crashed: 0
==========================================================
Timeout: Text/input/wpt-import/html/canvas/element/fill-and-stroke-styles/2d.pattern.basic.nocontext.html

This test was disabled in #3462