ci: group dependabot github action bump (#650)

reduce pull request noise for github action bump

Co-authored-by: Damien Mathieu <[email protected]>

Author: kruskall

.github/dependabot.yml

@@ -17,7 +17,9 @@ updates:
 
   # GitHub actions
   - package-ecosystem: "github-actions"
-    directory: "/"
+    directories:
+      - "/"
+      - "/.github/actions/*"
     reviewers:
       - "elastic/observablt-ci"
     schedule:
@@ -28,17 +30,3 @@ updates:
       github-actions:
         patterns:
           - "*"
-
-  # GitHub composite actions
-  - package-ecosystem: "github-actions"
-    directory: "/.github/actions/bootstrap"
-    schedule:
-      interval: "weekly"
-      day: "sunday"
-      time: "22:00"
-    reviewers:
-      - "elastic/observablt-ci"
-    groups:
-      github-actions:
-        patterns:
-          - "*"