ci: run ci weekly and allow for workflow dispatch

Author: MangoIV

.github/workflows/haskell-ci.yml

@@ -16,6 +16,9 @@ name: Haskell-CI
 on:
   - push
   - pull_request
+  - workflow_dispatch
+  - schedule:
+      - cron: '0 0 * * 0'
 jobs:
   linux:
     name: Haskell-CI - Linux - ${{ matrix.compiler }}