Do proper endian conversions

This fixes all testsuite failures on big endian hosts.

include/nlohmann/detail/output/binary_writer.hpp

@@ -1278,7 +1278,7 @@ class binary_writer
         std::memcpy(vec.data(), &n, sizeof(NumberType));
 
         // step 2: write array to output (with possible reordering)
-        if (is_little_endian and not OutputIsLittleEndian)
+        if (is_little_endian != OutputIsLittleEndian)
         {
             // reverse byte order prior to conversion if necessary
             std::reverse(vec.begin(), vec.end());