fix: simplify Dependabot config - remove npm ecosystem

- Remove npm package ecosystem (not applicable to GNOME extensions)
- Keep only GitHub Actions monitoring
- Fix YAML validation errors

Author: nickotmazgin

.github/dependabot.yml

@@ -1,19 +1,8 @@
 version: 2
 updates:
-  # Enable version updates for GitHub Actions (if any added later)
+  # Monitor GitHub Actions dependencies only
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
       interval: "monthly"
     open-pull-requests-limit: 3
-
-  # Monitor for any npm/node dependencies (if package.json exists)  
-  - package-ecosystem: "npm"
-    directory: "/"
-    schedule:
-      interval: "monthly"
-    open-pull-requests-limit: 2
-    ignore:
-      # Ignore development dependencies
-      - dependency-name: "*"
-        dependency-type: "development"