`./wpt run webkitgtk_minibrowser` is broken on Ubuntu 24.04

[mbrodesser-Igalia]

STR: ./wpt run --debug-test webkitgtk_minibrowser content-security-policy/navigation/javascript-url-navigation-evaluated-to-string-inherits-csp.html

Log:

./wpt run --debug-test webkitgtk_minibrowser content-security-policy/navigation/javascript-url-navigation-evaluated-to-string-inherits-csp.html 
Running 1 tests in web-platform-tests

  ▶ ERROR [expected OK] /content-security-policy/navigation/javascript-url-navigation-evaluated-to-string-inherits-csp.html
  │   → TypeError: undefined is not an object (evaluating 'cookies[i].split('=')[1].trim')
  │ 
  │ @http://web-platform.test:8000/content-security-policy/support/checkReport.sub.js:33:49
  └ global code@http://web-platform.test:8000/content-security-policy/support/checkReport.sub.js:138:3

Ran 1 tests finished in 14.4 seconds.
  • 0 ran as expected. 0 tests skipped.
  • 1 tests had errors unexpectedly

Works with "chrome" instead of "webkitgtk_minibrowser". Works neither with Firefox, see https://github.com/web-platform-tests/wpt/issues/49261.

[mbrodesser-Igalia]

This is not a multi-window issue, since e.g.

./wpt run --debug-test webkitgtk_minibrowser content-security-policy/navigation/to-javascript-url-script-src.html 
Running 1 tests in web-platform-tests

  [1/1] No tests running.

doesn't run the test.

[mbrodesser-Igalia]

$ MiniBrowser --version WebKitGTK 2.46.3