fix: readd missing config properties (#13716)

lib/workers/repository/process/index.ts

@@ -57,6 +57,11 @@ async function getBaseBranchConfig(
     baseBranchConfig.baseBranches = config.baseBranches;
   }
 
+  if (config.baseBranches.length > 1) {
+    baseBranchConfig.branchPrefix += `${baseBranch}-`;
+    baseBranchConfig.hasBaseBranches = true;
+  }
+
   baseBranchConfig = mergeChildConfig(baseBranchConfig, { baseBranch });
 
   return baseBranchConfig;