Reconfigure dependabot (RustPython#6158)

* Add `cargo` to dependabot

* Remove noisy comments

* Don't group updates

Author: ShaharNaveh

.github/dependabot.yml

@@ -1,13 +1,10 @@
-# Keep GitHub Actions up to date with GitHub's Dependabot...
-# https://docs.github.com/en/code-security/dependabot/working-with-dependabot/keeping-your-actions-up-to-date-with-dependabot
-# https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#package-ecosystem
 version: 2
 updates:
+  - package-ecosystem: cargo
+    directory: /
+    schedule:
+      interval: weekly
   - package-ecosystem: github-actions
     directory: /
-    groups:
-      github-actions:
-        patterns:
-          - "*"  # Group all Actions updates into a single larger pull request
     schedule:
       interval: weekly