.github/workflows/redmine-upkeep: remove concurrency limit

This now only runs on a 12h schedule so there isn't danger in overlap. The
long-running scheduled run also delays PR merge triggers (and may result in
cancellation of the PR merge run).

Signed-off-by: Patrick Donnelly <[email protected]>

Author: batrick

.github/workflows/redmine-upkeep.yml

@@ -31,9 +31,6 @@ on:
   push:
     branches:
       - 'feature/redmine-upkeep'
-concurrency:
-  group: redmine-upkeep-workflow-concurrency-group
-  cancel-in-progress: false
 jobs:
   redmine-upkeep:
     runs-on: ubuntu-latest