move ci to macos-latest

Author: stlankes

.github/workflows/build.yml

@@ -14,7 +14,7 @@ env:
 jobs:
   build:
     name: Build
-    runs-on: macos-11
+    runs-on: macos-latest
     steps:
     - uses: actions/checkout@v2
     - name: Install toolchain from rust-toolchain.toml