MessagePack reader: mark the initial accepted in the scalar run as a false-positive dead store

ci_infer reports DEAD_STORE for 'bool accepted = true;' in the MessagePack
scalar run, as in the CBOR one, because every case assigns accepted before it
is read.

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

include/nlohmann/detail/input/binary_reader.hpp

@@ -2657,6 +2657,8 @@ class binary_reader
             const auto* const data = reinterpret_cast<const unsigned char*>(ia.bulk_data());
             const unsigned char head = data[0];
             std::size_t size = 0;
+            // false positive: every case assigns accepted before it is read
+            // @infer-ignore DEAD_STORE
             bool accepted = true;
             switch (head)
             {