ci: run tests on latest node 19

[flovogt]

We're using ava and run tests against node 19. As of node > 19.5.0 the tests are failing because of

  TypeError [ERR_INVALID_ARG_TYPE]: The "payload" argument must be of type object. Received null

  › file:///home/runner/work/ui5-tooling-extensions/ui5-tooling-extensions/node_modules/mem/dist/index.js:42:27
  › file:///home/runner/work/ui5-tooling-extensions/ui5-tooling-extensions/node_modules/mem/dist/index.js:42:27

See full job details here https://github.com/SAP/ui5-tooling-extensions/actions/runs/4689838073/jobs/8312104201?pr=70

This PR enables ci tests for node 19 to ensure ava runs also smoothly on node 19.

[novemberborn]

Hadn't noticed we didn't add 19 when it came out. However Node.js 20 is due soon, and we won't be testing against 19 at that point.

I see the tests pass on 19 / Linux though. It's Windows that failed but it could just be flaky. If there is a bug, and you can fix it, then I'm happy to land that along with the CI coverage. Otherwise let's wait for 20.

[flovogt]

@novemberborn Thanks for your response. I've created #3194 which enables v20 in the test pipeline.