Disable Nix MacOS CI (unused and has upstream issue)

Author: dschrempf

.github/workflows/nix.yml

@@ -44,7 +44,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macOS-latest]
+        # TODO: Fix compilation problems on macOS.
+        # os: [ubuntu-latest, macOS-latest]
+        os: [ubuntu-latest]
 
     steps:
     - uses: actions/checkout@v3