Testing: No tests, if `test-wpt` broke again then we would notice pretty
quickly.
Fixes: https://github.com/servo/servo/issues/37124
---------
Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>
Most tests were only being run for layout-2013, not for layout-2020.
This wasn't great since layout-2020 is now the default.
So this patch unifies the lists of included tests for both layouts.
For layout-2013 this implies adding css/css-content/, css/css-logical/
and css/css-masking/clip/.
For layout-2020 this implies adding several additional css tests, and
also tests like dom/, js/, html/, etc.
