CI/Nix: build with submodules

- Clone repo recursively
- Update Nix install action
- Remove wlroots update

.github/workflows/nix-ci.yml

@@ -3,13 +3,12 @@ name: Nix
 on: [push, pull_request, workflow_dispatch]
 
 jobs:
-  wlroots:
-    if: github.event_name != 'pull_request'
-    uses: ./.github/workflows/nix-update-wlroots.yml
+  update-inputs:
+    uses: ./.github/workflows/nix-update-inputs.yml
     secrets: inherit
 
   build:
     if: always() && !cancelled() && !contains(needs.*.result, 'failure')
-    needs: wlroots
+    needs: update-inputs
     uses: ./.github/workflows/nix-build.yml
     secrets: inherit