fix(github): Fix System Tests Demo (#9)

Wrong location and invalid structure. Fixed.

Author: mmichaelis

demo/system-tests-demo.yml .github/workflows/system-tests-demo.ymldemo/system-tests-demo.yml renamed to .github/workflows/system-tests-demo.yml

@@ -10,9 +10,9 @@ jobs:
       matrix:
         os: [ubuntu-latest, macos-latest]
         install_gnu_tools: [true, false]
-      exclude:
-        - os: ubuntu-latest
-          install_gnu_tools: true
+        exclude:
+          - os: ubuntu-latest
+            install_gnu_tools: true
 
     steps:
       - name: Checkout repository