Fix invalid prop warning in On-demand scans

ee/app/assets/javascripts/on_demand_scans/components/on_demand_scans_app.vue

@@ -17,7 +17,8 @@ export default {
     },
     defaultBranch: {
       type: String,
-      required: true,
+      required: false,
+      default: '',
     },
     emptyStateSvgPath: {
       type: String,

ee/app/assets/javascripts/on_demand_scans/components/on_demand_scans_form.vue

@@ -91,7 +91,8 @@ export default {
     },
     defaultBranch: {
       type: String,
-      required: true,
+      required: false,
+      default: '',
     },
   },
   inject: {

ee/changelogs/unreleased/djadmin-dast-branch-warning.yml

+---
+title: Fix invalid prop warning in On-demand scans
+merge_request: 49472
+author:
+type: fixed