Fix editor accessibility test

[khanniie]

Fixes the editor accessibility issue that appears to happen on the develop branch:

 FAIL  client/modules/IDE/components/EditorAccessibility.unit.test.jsx
  ● <EditorAccessibility /> › renders empty message with no lines

    TestingLibraryElementError: Unable to find an accessible element with the role "listitem" and description "There are no lint messages"

Changes: The issue (not sure when it was first introduced) is that the "there are no lint messages" list item element does not have an aria-describedby attribute so the original method of fetching by role and description does not actually detect what it's looking for. This switches the test to look for the string instead.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

[release-com]

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• p5.js-web-editor
  • app-tedc5fb.release.editor.p5js.org/
  • preview-tedc5fb.release.editor.p5js.org/

🔧Environment Status : https://app.release.com/public/Processing%20Foundation/env-a55ba451c5