Tests: Disable a few tests that regularly flake on CI

Author: AtkinsSJ

Tests/LibWeb/TestConfig.ini

@@ -342,3 +342,12 @@ Text/input/input-file.html
 ; Times out due to `document.adoptNode` invocation
 ; https://github.com/LadybirdBrowser/ladybird/issues/6150
 Crash/wpt-import/css/css-view-transitions/first-line-reparent-crash.html
+
+; Flaky: https://github.com/LadybirdBrowser/ladybird/issues/6299
+Text/input/GamepadAPI/gamepad-rumble.html
+
+; Flaky: https://github.com/LadybirdBrowser/ladybird/issues/6300
+Text/input/wpt-import/html/semantics/popovers/popover-toggle-source.tentative.html
+
+; Flaky: https://github.com/LadybirdBrowser/ladybird/issues/5257
+Text/input/selection-over-multiple-code-units.html