Update ubuntu-20.04 to ubuntu-latest in GitHub workflow

Co-authored-by: pamelafox <[email protected]>

Author: Copilot

.github/workflows/tests.yaml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: ["ubuntu-20.04"]
+        os: ["ubuntu-latest"]
         python_version: ["3.9", "3.10", "3.11", "3.12"]
     services:
       postgres: