Update release workflow to use latest Ubuntu instead of 18.04

Author: lemonsaurus

.github/workflows/release.yml

@@ -7,7 +7,7 @@ on:
 jobs:
   build:
     name: Build dist & publish
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
 
     steps:
     - name: Checkout the repo and the submodules.