Add more dependabot groups (#286)

This is part of a series of commits across several repositories in order
to group development dependencies.  The logic is that often these
dependencies are safer to upgrade as they are not used in production.
Furthermore, CI is much more likely to fail if there are any problems or
incompatibilities.

Author: slifty

.github/dependabot.yml

@@ -23,3 +23,7 @@ updates:
       timezone: "Etc/UTC"
     cooldown:
       default-days: 7
+    groups:
+      github-actions:
+        patterns:
+          - "*"