Use a environment variable to check each system

Co-authored-by: Florian Sesser <[email protected]>
Signed-off-by: Benoit Donneaux <[email protected]>

.github/workflows/nix.yml

@@ -14,12 +14,17 @@ on:
       - 'nix/**'
       - 'flake.*'
 
+env:
+  # This define the targeted systems we want to check (and later deploy) the nixosConfiguration
+  MATRIX: |
+    matrix={"include":[
+      {"target":"webforge","hostname":"webforge","domain":"tahoe-lafs.org"}
+    ]}
+
 jobs:
   check:
     name: Check
     runs-on: ubuntu-24.04
-    outputs:
-      matrix: ${{ steps.set-matrix.outputs.matrix }}
     steps:
       - name: Checkout
         id: checkout
@@ -35,19 +40,14 @@ jobs:
           nix flake show
           nix flake check
 
-      - name: Set matrix
-        id: set-matrix
-        run: |
-          echo 'matrix={"include":[{"target":"webforge","hostname":"webforge","domain":""}]}' >> $GITHUB_OUTPUT
-
   build:
     name: Build
     runs-on: ubuntu-24.04
     if: github.event_name == 'pull_request'
     needs: check
     strategy:
       fail-fast: false
-      matrix: ${{fromJson(needs.check.outputs.matrix)}}
+      matrix: ${{ env.MATRIX }}
     steps:
       - name: Checkout
         id: checkout