Update backport-starting-v511.yml (#301)

Author: cheels

.github/workflows/backport-starting-v511.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        branch: ['v/5.11','v/5.12','v/5.13','v/5.14']
+        branch: ['v/5.11','v/5.12','v/5.13','v/5.14','v/5.15']
     uses: hazelcast/hz-docs/.github/workflows/backport-workflow.yml@main
     with:
       label-to-check-for: '["backport starting from 5.11"]'

.github/workflows/backport.yml

@@ -7,7 +7,7 @@ jobs:
   get-maintenance-branches:
     runs-on: ubuntu-latest
     outputs:
-      branches: "['5.8', '5.9', '5.10', '5.11', '5.12', '5.13', '5.14']"
+      branches: "['5.8', '5.9', '5.10', '5.11', '5.12', '5.13', '5.14','5.15']"
     steps:
       - run: exit 0