Unified let syntax to be a list of objects

doc/manual/sphinx/source/test_items/let_test_item.rst

@@ -9,9 +9,9 @@ This element is of the following form:
     - let:
         name: Let Item
         values:
-            key1: value1
-            key2: value2
-            key3: <| $(variable)[$(loop_index)] |>
+            - key1: value1
+            - key2: value2
+            - key3: <| $(variable)[$(loop_index)] |>
 
 The ``let`` element is used to set values in the global directory.
 

doc/manual/sphinx/source/tum_syntax.rst

@@ -51,8 +51,8 @@ The parameter file can be specified in the `.tum` file root:
     :caption: configuration files definition in the main `.tum` test file
 
     config_file:
-        config1.yaml
-        config2.yaml
+        - config1.yaml
+        - config2.yaml
 
     main:
         name: Test example