ci: add a shellcheck workflow

This  initializes the CI for this repo

Signed-off-by: Michael Adam <obnox@samba.org>

Author: obnoxxx

.github/workflows/shellcheck.yaml

@@ -0,0 +1,33 @@
+name: ShellCheck
+on:
+  push:
+    tags:
+      - v*
+    branches:
+      - main
+      - release-*
+  pull_request:
+    branches:
+      - main
+      - release-*
+
+# cancel the in-progress workflow when PR is refreshed.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && github.head_ref || github.sha }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  shellcheck:
+    name: Shellcheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+      - name: install shellcheck
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y shellcheck
+      - name: Run ShellCheck
+        run: make shellcheck