Fix clang-tidy readability-redundant-member-init in BSON test

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

tests/src/unit-bson.cpp

@@ -1311,7 +1311,7 @@ TEST_CASE("BSON declared document size bounds the content")
     // records the events that a SAX parser receives
     struct recorder : nlohmann::json_sax<json>
     {
-        std::string events {};
+        std::string events;
 
         bool null() override
         {