Update gather-docs.yaml's branch name to the release branch

Author: imodeljs-admin

common/config/azure-pipelines/templates/gather-docs.yaml

@@ -112,6 +112,6 @@ steps:
       project: 2c48216e-e72f-48b4-a4eb-40ff1c04e8e4
       pipeline: 7436 # iTwin.js/Docs/iTwin.js Docs - YAML
       buildVersionToDownload: latestFromBranch
-      branchName: refs/heads/release/5.5.x
+      branchName: refs/heads/release/5.6.x
       artifactName: .updated.json
       targetPath: ${{ parameters.stagingDir }}/config/