project: use macOS-12 as a runner

Author: twittemb

.github/workflows/ci.yml

@@ -5,12 +5,9 @@ on: [push]
 jobs:
   build:
 
-    runs-on: macos-latest
+    runs-on: macos-12
 
     steps:
-      - uses: swift-actions/setup-swift@v1
-        with:
-          swift-version: "5.6.1"
       - uses: actions/checkout@v3
       - name: Build
         run: swift build