ci: disable dependabot auto-PRs (#14)

Co-authored-by: Srikanth Patchava <Srikanth.Patchava@brooksautomation.com>

Author: srpatcha

.github/dependabot.yml

@@ -1,22 +1,9 @@
+# Dependabot disabled — dependency updates are managed manually.
+# To re-enable, set open-pull-requests-limit to a positive number.
 version: 2
 updates:
   - package-ecosystem: "github-actions"
-    directory: "/"
-    schedule:
-      interval: "weekly"
-      day: "monday"
-    labels:
-      - "dependencies"
-      - "ci"
-    commit-message:
-      prefix: "ci"
-
-  - package-ecosystem: "gitsubmodule"
     directory: "/"
     schedule:
       interval: "monthly"
-    labels:
-      - "dependencies"
-      - "submodule"
-    commit-message:
-      prefix: "deps"
+    open-pull-requests-limit: 0