[test] Check a11y tree inclusion in CI only

[eps1lon]

Skip isAccessible check by default but verify this assumption in CI

Rationale: https://github.com/eps1lon/material-ui/blob/test/faster-local/CONTRIBUTING.md#accessiblity-tree-exclusion

[mui-pr-bot]

No bundle size changes comparing 15e3336...00166f2

Generated by 🚫 dangerJS against 00166f2

[oliviertassinari]

Before > 2639 passing (50s)
After > 2637 passing (30s)

For curiosity, I have tried this diff, same output:

diff --git a/node_modules/@testing-library/dom/dist/role-helpers.js b/node_modules/@testing-library/dom/dist/role-helpers.js
- if (window.getComputedStyle(element).display === 'none') {
+ if (({}).display === 'none') {
    return true;
  }

...


- if (window.getComputedStyle(element).visibility === 'hidden') {
+ if (({}).visibility === 'hidden') {
    return true;
  }

Great job! Performance issue with testing-library: solved 👏.