test: fix flaky test in literal expression

[barmac]

Proposed Changes

This attempts to fix the flaky test which has been causing build failures for a while, e.g. https://github.com/bpmn-io/dmn-js/actions/runs/11365121269/job/31612772137?pr=909

Checklist

To ensure you provided everything we need to look at your PR:

• Brief textual description of the changes present
• Visual demo attached
• Steps to try out present, i.e. using the @bpmn-io/sr tool
• Related issue linked via Closes {LINK_TO_ISSUE} or Related to {LINK_TO_ISSUE}

[barmac]

I included d452c8a in this PR so that CI can be green.

[barmac]

It doesn't fix the problem 🙈

[barmac]

There's another flaky test in the project :D
https://github.com/bpmn-io/dmn-js/actions/runs/11366421982/job/31616761294?pr=910#step:5:1127

[barmac]

I've reworked the test to use the API as there's no need to fiddle with DOM elements.

[nikku]

Great changes 🥇