scripts: support windows/cygwin

[benthillerkus]

cygwin ships with Git for Windows, so most Windows dev machines should have this.

I considered rewriting the scripts to use a command runner like casey/just or cargo-make, but tbh this suffices.

• For the web-wasm script I removed the Linux path as it seems to have not actually build a wasm target.
• The test.sh script seems to have been broken without the --scene parameter. Maybe the Godot CLI changed over time here.