.github/workflows/development.yaml: back out 3.9 config

Author: Chris Turner

.github/workflows/development.yaml

@@ -14,11 +14,9 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        py_ver: ["3.9"]
+        py_ver: ["3.8"]
         mysql_ver: ["8.0", "5.7", "5.6"]
         include:
-          - py_ver: "3.8"
-            mysql_ver: "5.7"
           - py_ver: "3.7"
             mysql_ver: "5.7"
           - py_ver: "3.6"