nix: switched over to the new submodules flake attribute

In the latest release of Nix, one can now declare that they'd like
submodules included within the flake files inputs.

Author: HU90m

.github/workflows/ci.yml

@@ -33,15 +33,15 @@ jobs:
         run: nix fmt -- . --check --exclude ./third_party --exclude ./cheriot-rtos
 
       - name: Run Lints
-        run: nix run .?submodules=1#lint-all
+        run: nix run .#lint-all
 
       - name: Build Software
         run: |
-          nix build -L .?submodules=1#sonata-exercises
-          nix build -L .?submodules=1#sonata-examples
-          nix build -L .?submodules=1#sonata-automotive-demo-legacy-component
-          nix build -L .?submodules=1#sonata-heartbleed-demo-legacy-component
-          nix build -L .?submodules=1#sonata-tests
+          nix build -L .#sonata-exercises
+          nix build -L .#sonata-examples
+          nix build -L .#sonata-automotive-demo-legacy-component
+          nix build -L .#sonata-heartbleed-demo-legacy-component
+          nix build -L .#sonata-tests
 
       - name: Run Nix Checks
-        run: nix flake check -L .?submodules=1#
+        run: nix flake check -L .#

flake.nix

@@ -3,6 +3,7 @@
 {
   description = "Sonata software";
   inputs = {
+    self.submodules = true;
     sonata-system.url = "github:lowRISC/sonata-system";
     lowrisc-nix.follows = "sonata-system/lowrisc-nix";
     nixpkgs.follows = "lowrisc-nix/nixpkgs";