fix: pr should be ensured if branch automerge previously failed

If branch automerge *previously* failed, then still make sure we are keeping the PR up to date.

Closes #1336

lib/workers/branch/index.js

@@ -135,7 +135,11 @@ async function processBranch(branchConfig) {
     if (mergeStatus === 'automerged') {
       logger.debug('Branch is automerged - returning');
       return 'automerged';
-    } else if (mergeStatus === 'failed') {
+    } else if (
+      mergeStatus === 'automerge aborted - PR exists' ||
+      mergeStatus === 'failed'
+    ) {
+      logger.info({ mergeStatus }, 'Branch automerge not possible');
       config.forcePr = true;
     }
   } catch (err) {