Remove ubuntu-20.04 in favor of ubuntu-22.04 for Python 3.7

Author: dbieber

.github/workflows/build.yml

@@ -18,7 +18,7 @@ jobs:
         os: ["macos-latest", "ubuntu-latest"]
         python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13.0-rc.2"]
         include:
-          - {os: "ubuntu-20.04", python-version: "3.7"}
+          - {os: "ubuntu-22.04", python-version: "3.7"}
 
     steps:
      # Checkout the repo.