a1515cdd96 ci: use Ubuntu Jammy for Windows CI (fanquake)
Pull request description:
This means we'll compile using [GCC 10.3.x](https://packages.ubuntu.com/jammy/g++-mingw-w64) and [mingw-w64 8.0.0](https://packages.ubuntu.com/jammy/mingw-w64) which better matches our Guix release environment.
ACKs for top commit:
MarcoFalke:
cr ACK a1515cdd96
hebasto:
ACK a1515cdd96, I have reviewed the code and it looks OK, I agree it can be merged.
Tree-SHA512: a57cce1874324c9dd00e5d8989996d214facbdd561440471c15e6cc1808bca1c6fd758abe7a1b87378b2e7f9c25e7c9d8242df911cd1ef6cfbe49718adc3be5d