ci: fix pro_impl branch

Author: fiftin

.github/workflows/pro_selfhosted_beta.yml

@@ -39,7 +39,7 @@ jobs:
 
       - name: Add PRO implementation
         run: |
-          git clone https://${{ secrets.GH_TOKEN }}@github.com/semaphoreui/semaphorepro-module.git pro_impl
+          git clone -b 2-17-stable https://${{ secrets.GH_TOKEN }}@github.com/semaphoreui/semaphorepro-module.git pro_impl
           go work init . ./pro_impl
 
       - name: Install deps