Revert "refactor(gitlab): always debug merge err"

This reverts commit 6237a7f4.

lib/platform/gitlab/index.js

@@ -770,7 +770,6 @@ async function mergePr(iid) {
     });
     return true;
   } catch (err) /* istanbul ignore next */ {
-    logger.debug({ err }, 'merge PR error');
     if (err.statusCode === 401) {
       logger.info('No permissions to merge PR');
       return false;
@@ -779,6 +778,7 @@ async function mergePr(iid) {
       logger.info('PR not acceptable for merging');
       return false;
     }
+    logger.debug({ err }, 'merge PR error');
     logger.info('PR merge failed');
     return false;
   }