Bump lowest test version to Python 3.8

Closes #2827

Author: jeromekelleher

.github/workflows/tests.yml

@@ -60,7 +60,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python: [ 3.7, 3.9, "3.11" ]
+        python: [ 3.8, 3.9, "3.11" ]
         os:  [ macos-latest, ubuntu-latest, windows-latest ]
     defaults:
       run: