Remove non-Nix macOS builds from CI

.github/workflows/ci.yaml

@@ -11,7 +11,7 @@ jobs:
       matrix:
         ghc: ['9.2.8']
         cabal: ['3.10']
-        os: ['ubuntu-20.04', 'ubuntu-22.04', 'macOS-latest']
+        os: ['ubuntu-20.04', 'ubuntu-22.04']
 
     steps:
     - name: 'GitHub actions env workaround'
@@ -41,11 +41,6 @@ jobs:
           dist-newstyle
         key: ${{ matrix.os }}-${{ matrix.ghc }}-4-cabal
 
-    # System dependencies
-    - name: Install liblzma
-      run: brew install xz # xz package contains liblzma
-      if: startsWith(matrix.os, 'macOS')
-
     # Build
     - name: Update package database
       run: cabal update