listgen: remove EOL pythons

This leaves only 3.9 on the legacy listgen, meaning
we can remove it entirely next year.

Signed-off-by: William Woodruff <[email protected]>

Author: woodruffw

.github/workflows/listgen.yml

@@ -15,8 +15,6 @@ jobs:
     strategy:
       matrix:
         python:
-          - "3.7"
-          - "3.8"
           - "3.9"
 
     runs-on: ubuntu-latest