ensure generate_matrix.py outputs valid JSON for fromJSON() and fix YAML upload indentation

Author: Jeevan Revaneppa Hirethanad

.github/workflows/scripts/generate_matrix.py

@@ -27,12 +27,12 @@ def main():
         for board in boards:
             rows.append({
                 "app": app,
-                "board": board,
+                "board": board
             })
 
     if not rows:
         # Avoid empty matrix which makes Actions error out
-        rows = {"app":"noop","board":"noop"}
+        rows = [{"app":"noop","board":"noop"}]
 
     matrix = {"include": rows}
     print(json.dumps(matrix, indent=2))