CI: Disable "Nightly" testing on macOS

CrateDB does not produce nightly tarballs for macOS.

Author: amotl

.github/workflows/nightly.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: ['ubuntu-20.04', 'ubuntu-22.04', 'macos-11', 'macos-12']
+        os: ['ubuntu-20.04', 'ubuntu-22.04']  # 'macos-11', 'macos-12'
         python-version: ['3.7', '3.8', '3.9', '3.10', '3.11-dev']
         cratedb-version: ['nightly']
         sqla-version: ['latest']