chore(zed): group dependabot updates per ecosystem (#5)

Bundle cargo + github-actions bumps into one weekly grouped PR (Dependabot groups), so
updates that share a lockfile land atomically instead of conflicting when
merged serially under branch protection.

Author: lgogolin

.github/dependabot.yml

@@ -4,7 +4,15 @@ updates:
     directory: "/"
     schedule:
       interval: weekly
+    groups:
+      cargo-deps:
+        patterns:
+          - "*"
   - package-ecosystem: github-actions
     directory: "/"
     schedule:
       interval: weekly
+    groups:
+      actions:
+        patterns:
+          - "*"