ci: Add a shellcheck workflow, and fix SC2086 in develop

Signed-off-by: Gergely Nagy <me@gergo.csillger.hu>

.forgejo/workflows/shellcheck.yaml

@@ -0,0 +1,30 @@
+---
+name: Shellcheck
+
+on:
+  push:
+    paths:
+      - '**/bin/*'
+      - '.forgejo/workflows/shellcheck.yaml'
+
+jobs:
+  shellcheck:
+    runs-on: nixos-flakes
+
+    steps:
+      - name: checkout
+        uses: actions/checkout@v3
+
+      - name: install shellcheck
+        uses: ./shell
+        with:
+          flake: nixpkgs
+          package: shellcheck
+
+      - name: shellcheck all our scripts
+        uses: ./shell
+        with:
+          flake: nixpkgs
+          package: shellcheck
+          run: |
+            shellcheck **/bin/*

develop/bin/nix-develop

@@ -6,7 +6,7 @@ trap 'rm -rf "$workdir"' EXIT
 echo "${INPUT_RUN}" >"${workdir}/run.sh"
 
 __cmd="develop"
-if [ "$(basename $0)" = "nix-shell" ]; then
+if [ "$(basename "$0")" = "nix-shell" ]; then
     __cmd="shell"
 fi