Fix vector constructor ambiguity in H5DataType.hpp (#775)

Updated the code in H5DataType.hpp to fix the compilation error caused by a vector constructor ambiguity when _GLIBCXX_DEBUG is defined. Replaced std::vector<member_def>({t_members}) with std::vector<member_def>(t_members) to eliminate unnecessary copy constructor calls.

include/highfive/H5DataType.hpp

@@ -250,7 +250,7 @@ class EnumType: public DataType {
     }
 
     EnumType(std::initializer_list<member_def> t_members)
-        : EnumType(std::vector<member_def>({t_members})) {}
+        : EnumType(std::vector<member_def>(t_members)) {}
 
     /// \brief Commit datatype into the given Object
     /// \param object Location to commit object into