chore: improve logging for stale branch rebase

lib/util/git/index.ts

@@ -520,6 +520,7 @@ export async function isBranchModified(branchName: string): Promise<boolean> {
     config.ignoredAuthors.some((ignoredAuthor) => lastAuthor === ignoredAuthor)
   ) {
     // author matches - branch has not been modified
+    logger.debug({ branchName }, 'Branch has not been modified');
     config.branchIsModified[branchName] = false;
     return false;
   }

lib/workers/branch/reuse.ts

@@ -60,6 +60,7 @@ export async function shouldReuseExistingBranch(
         logger.debug('Cannot rebase branch as it has been modified');
         return { reuseExistingBranch: true, isModified: true };
       }
+      logger.debug('Branch has no changes, but we will not use it');
       return { reuseExistingBranch: false };
     }
     logger.debug('Branch is up-to-date');