Build: Invert JSX pragma application condition

[aduth]

Related: #7493

This pull request seeks to resolve an issue where making changes to a packages file which includes JSX will cause the JSX pragma to not be injected correctly, resulting in errors when reloading the editor after the rebuild completes. This is because the watch task for plugin build runs a rebuild in a subprocess which does not inherit the TRANSFORM_JSX_PRAGMA environment variable used to include the plugin necessary for pragma injection.

The changes in this pull request invert the condition to a "skip" environment variable, used exclusively in the prebuild step for transpiling the babel-plugin-import-jsx-pragma package.

Testing instructions:

1. Run npm run dev
2. Make a change to packages/data/src/index.js and save the file
3. Reload the editor once the rebuild has completed
4. Observe there are no errors

[gziolo]

Yes, it makes sense as in fact we want to skipt it for itself. I will test it later today.

[gziolo]

Tests well 🚢