ignore dependabot in release drafter (#1537)

Author: maekawataiki

.github/release-drafter.yml

@@ -19,6 +19,9 @@ version-resolver:
     labels:
       - 'patch'
   default: patch
+exclude-contributors:
+  - 'dependabot'
+  - 'dependabot[bot]'
 exclude-labels:
   - 'new release'
 template: |