Add link to issue on non-testability of the Dynamic Code Brand Checks proposal

[ioannad]

Following up on @ljharb's suggestion #535 (comment)

[nicolo-ribaudo]

Maybe we could link to WPT tests instead? The discussion in plenary was "this cannot be tested in test262, but we approve stage 2.7 because it's at least tested in WPT".

[ioannad]

@nicolo-ribaudo are there WPT tests already? If not, we could add a link to them later either here or in the test262 issue.

[nicolo-ribaudo]

cc @lukewarlow :)

[lukewarlow]

https://wpt.fyi/results/trusted-types?label=master&label=experimental&aligned&q=eval this shows the various test files that test TT with eval.

https://github.com/web-platform-tests/wpt/blob/master/trusted-types%2Feval-csp-no-tt.html this is probably the one closest to testing the pure tc39 aspect of this.