Now that we are using Focal for gitian builds, and have NSIS 3.0+ available (also in Guix), we can create installers that support unicode. Unicode is only becoming the default beginning with the 3.07 release, https://nsis.sourceforge.io/Docs/AppendixF.html#v3.07-cl, so we need to set this attribute to get support. Should close: #13817
On Debian 10 the nsis version is 3.04, so we should be able to use the
feature.
Backport of core#21333