Removed duplicated curly braces in test stubs too

tests/test_paperqa.py

@@ -641,7 +641,7 @@ def test_custom_json_props():
         summary_json_system="Provide a summary of the excerpt that could help answer the question based on the excerpt.  "  # noqa: E501
         "The excerpt may be irrelevant. Do not directly answer the question - only summarize relevant information. "
         "Respond with the following JSON format:\n\n"
-        '{{\n"summary": "...",\n"person_name": "...",\n"relevance_score": "..."}}\n\n'
+        '{\n"summary": "...",\n"person_name": "...",\n"relevance_score": "..."}\n\n'
         "where `summary` is relevant information from text - "
         "about 100 words words, `person_name` specifies the person discussed in "
         "the excerpt (may be different than query), and `relevance_score` is "