Merge #11029

11029: internal: Refactor release workflow to reduce duplication r=lnicola a=lnicola

This reduces duplication by using `matrix` and paves the way for #10483. The `musl` builder is unchanged because it uses a container.

~~We also get rid of the MacOS 11 SDK thing, which is from when most MacOS builders were on 10.~~ Or not, the default is still 10.15.

Co-authored-by: Laurențiu Nicola <[email protected]>

Author: bors[bot]