Group Dependabot version updates

So related actions, such as upload-artifact and download-artifact,
get updates together. This should allow the PRs to pass CI, and
also avoid a situation (if the check failures were disregarded)
where an intermediate state where some updates have been accepted
and others have not would break CI on main.

Author: EliahKagan

.github/dependabot.yml

@@ -4,4 +4,6 @@ updates:
     directory: "/"
     schedule:
       interval: weekly
-    open-pull-requests-limit: 3
+    groups:
+      github-actions:
+        patterns: ["*"]