maint(web): additionally run web builds on Windows build agents 🎼

Currently we build web only on one build agent. This has occasionally has lead to the situation where a PR built on a Linux agent and got merged, but then the master branch got built on a Windows agent and failed.

We should change our builds so that Web builds on all platforms, similar to what we already do for Core.

This should be done only after epic/web-core merged since that significantly reduces the build time of web.