fix node.trigger return type to handle undefined values

[m4thieulavoie]

Description

Fixes (issue #)

After the changes made lately to the typings of .trigger, a Function | undefined would not be resolved. This PR adds support for that to properly resolve it. Hacking that in the typings of react-testing in web's node_modules made yarn type-check pass properly.

Note that I could've removed the NonNullable<> syntax, but I figured we still want to exclude null. Happy to change if it makes more sense though

Type of change

• Patch: Bug (non-breaking change which fixes an issue)
• Minor: New feature (non-breaking change which adds functionality)
• Major: Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added a changelog entry, prefixed by the type of change noted above (Documentation fix and Test update does not need a changelog as we do not publish new version)

[BPScott]

Thanks for testing this! Code looks great.

One note inline to add the PR number to the changelog entry