chore/update-ubuntu (#1008)

Bumping ubuntu runner to `-latest` as 20.04 is EOL.

Author: tkyocum

.github/workflows/pr.yml

@@ -7,7 +7,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
 
     strategy:
       matrix: