Disable all Dependabot updates apart from security ones

As done in alphagov/content-publisher#3287 and alphagov/maslow#1293, we want to disable Dependabot PRs for this deprecated repo.

Author: ChrisBAshton

.github/dependabot.yml

@@ -5,16 +5,16 @@ updates:
     schedule:
       interval: daily
       time: "03:00"
-    open-pull-requests-limit: 10
+    open-pull-requests-limit: 0
   - package-ecosystem: npm
     directory: "/"
     schedule:
       interval: daily
       time: "03:00"
-    open-pull-requests-limit: 10
+    open-pull-requests-limit: 0
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
       interval: daily
       time: "03:00"
-    open-pull-requests-limit: 10
+    open-pull-requests-limit: 0