CI: run shellcheck

.github/workflows/shellcheck-exceptions.txt

@@ -0,0 +1,2 @@
+.github/bin/haddocks.sh
+scripts/ci/check-cabal-files.sh

.github/workflows/shellcheck.yml

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+name: Shellcheck
+
+on:
+  pull_request:
+  push:
+    branches:
+      - smelc/release-create-changelog
+
+jobs:
+  example:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install Nix with good defaults
+        uses: input-output-hk/install-nix-action@v20
+        with:
+          extra_nix_config: |
+            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=
+            substituters = https://cache.iog.io/ https://cache.nixos.org/
+          nix_path: nixpkgs=channel:nixos-unstable
+      - uses: cachix/install-nix-action@v18
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      # To make the environment in your flake's devShell available to future
+      # steps:
+      - uses: rrbutani/use-nix-shell-action@v1
+      - name: Shellcheck
+        run: |
+          for file in $(git ls-files "*.sh")
+          do
+            if grep -q "$file" .github/workflows/shellcheck-exceptions
+            then
+              echo "⚠️ $file is ignored from shellcheck's verifications. Please consider fixing it."
+            else
+              shellcheck "$file"
+            fi
+          done