Add required tag to new tests

Author: pvanheus

conformance_tests.yaml

@@ -3405,18 +3405,18 @@
   label: params_broken_null
   doc: Test parameter reference that refers to null.something
   should_fail: true
-  tags: [ command_line_tool ]
+  tags: [ required, command_line_tool ]
 
 - job: tests/empty.json
   tool: tests/params_broken_length_of_non_list.cwl
   doc: Test paramer reference that refers to length of non-array input
   should_fail: true
-  tags: [ command_line_tool ]
+  tags: [ required, command_line_tool ]
 
 - job: tests/length_non_array_input.yml
   tool: tests/params_input_length_non_array.cwl
   doc: Test 'length' in parameter reference where it does not refer to length of an array input
-  tags: [ command_line_tool ]
+  tags: [ required, command_line_tool ]
   output:
     output1: 1
     output2: 2