Run shellcheck in CI

.gitea/workflows/shellcheck.yml

@@ -0,0 +1,18 @@
+on:
+  workflow_call:
+  push:
+    branches:
+      - main
+  pull_request:
+  schedule:
+    - cron: '0 0 * * *'
+
+jobs:
+  shellcheck:
+    name: Check scripts
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: https://gitea.com/actions/checkout@v4
+      - name: Run shellcheck
+        run: shellcheck ./container/*.sh