Running yarn why eslint-plugin-jsx-a11y returns
├─ @plone/volto@npm:17.15.0
│ └─ eslint-plugin-jsx-a11y@npm:6.7.1 [51660] (via npm:6.7.1 [51660])
│
├─ eslint-config-react-app@npm:7.0.1
│ └─ eslint-plugin-jsx-a11y@npm:6.8.0 (via npm:^6.5.1)

We get the following error which breaks eslint testing
Error: Plugin "jsx-a11y" was conflicted between ".eslintrc.js » ./node_modules/@plone/volto/.eslintrc" and ".eslintrc.js » ./node_modules/@plone/volto/.eslintrc » eslint-config-react-app".