feat: run build and flakes jobs on more OS-s (#291)

Author: deemp

.github/workflows/nix.yml

@@ -11,7 +11,7 @@ jobs:
   build:
     strategy:
       matrix:
-        os: [ ubuntu-20.04, macos-latest ]
+        os: [ ubuntu-20.04, ubuntu-22.04, macos-11, macos-12 ]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
@@ -28,7 +28,7 @@ jobs:
   flakes:
     strategy:
       matrix:
-        os: [ ubuntu-20.04 ] # macos-latest is not working right now
+        os: [ ubuntu-20.04, ubuntu-22.04, macos-11, macos-12 ]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4