fix: populate isLockFileMaintenance (#14005)

Lock file maintenance was broken as various managers rely on the
`isLockFileMaintenance` update flag to be set. This was not the
case as its config is generated afterwards (without the is*
auto-propagation).

lib/workers/repository/updates/flatten.spec.ts

@@ -179,7 +179,10 @@ describe('workers/repository/updates/flatten', () => {
         res.filter((update) => update.sourceRepoName)[2].sourceRepoName
       ).toBe('node');
       expect(
-        res.filter((r) => r.updateType === 'lockFileMaintenance')
+        res.filter(
+          (r) =>
+            r.updateType === 'lockFileMaintenance' && r.isLockFileMaintenance
+        )
       ).toHaveLength(2);
       expect(res.filter((r) => r.isVulnerabilityAlert)).toHaveLength(1);
     });

lib/workers/repository/updates/flatten.ts

@@ -140,6 +140,7 @@ export async function flattenUpdates(
           packageFileConfig.lockFileMaintenance
         );
         lockFileConfig.updateType = 'lockFileMaintenance';
+        lockFileConfig.isLockFileMaintenance = true;
         lockFileConfig = applyPackageRules(lockFileConfig);
         // Apply lockFileMaintenance and packageRules again
         lockFileConfig = mergeChildConfig(