Update Nix shell and add envrc

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ on:
 
 jobs:
   shellcheck:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
         with:
@@ -16,4 +16,4 @@ jobs:
       - name: Enable magic Nix cache
         uses: DeterminateSystems/magic-nix-cache-action@main
       - name: Shellcheck
-        run: nix-shell --run 'shellcheck $(find . -type f -name "*.sh" -executable)'
+        run: nix develop --command shellcheck $(find . -type f -name "*.sh" -executable)