Fix "Invalid JSON configuration, must be a dict" (apache#16648)

Wrong variable name used

(cherry picked from commit c975d4c)
(cherry picked from commit 4157346)

airflow/www/views.py

@@ -1524,7 +1524,7 @@ def trigger(self, session=None):
         if request_conf:
             try:
                 run_conf = json.loads(request_conf)
-                if not isinstance(conf, dict):
+                if not isinstance(run_conf, dict):
                     flash("Invalid JSON configuration, must be a dict", "error")
                     return self.render_template(
                         'airflow/trigger.html', dag_id=dag_id, origin=origin, conf=request_conf