Bump Ubuntu release (#150)

GitHub deprecating Ubuntu 20.04:
actions/runner-images#11101

Author: morancj

.github/workflows/rust.yaml

@@ -11,7 +11,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - name: Check-out code
         uses: actions/checkout@v2