Configure Dependabot to group updates

Add grouping for Dependabot updates to combine into a single PR.

.github/dependabot.yml

diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index d5e7fb7..4e5d64d 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -9,3 +9,8 @@
     directory: "/"
     schedule:
       interval: "weekly"
+    # Combine updates into single PR
+    groups:
+      everything:
+        patterns:
+          - "*" # Everything