test(tools): cover non-object JSON in concatenated arguments

Codecov flagged the `not isinstance(obj, dict)` guard in
`_split_complete_json_objects` as the one uncovered line in the patch.
`{"a": 1}[1, 2]` decodes cleanly but yields a list, which must not be
salvaged as tool arguments.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_litellm/litellm_core_utils/prompt_templates/test_litellm_core_utils_prompt_templates_common_utils.py

@@ -315,6 +315,7 @@ def test_parse_tool_call_arguments_concatenated_is_not_dropped_silently():
         '{"a": 1}{"b":',  # truncated tail
         '{"a": 1} garbage',  # trailing garbage
         '{"a": 1}{"b": 2} x',  # complete objects followed by junk
+        '{"a": 1}[1, 2]',  # valid JSON, but not an object
     ],
 )
 def test_parse_tool_call_arguments_rejects_incomplete_concatenation(raw):