try switching to ubuntu-latest gh runner to fix gh action - again

Author: maximevanhees

.github/workflows/rust.yml

@@ -4,7 +4,7 @@ on: [push]
 
 jobs:
   build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v1
         name: Checkout code