Use memcpy instead of strncpy in GCodeFormatter::emit_string() to silence the warning.

The warning was there because std::string_view::data() returns a pointer to a buffer that is not necessarily null-terminated. So, strncpy shouldn't be used on non-null-terminated buffers, but we always relied only on the buffer length, so it couldn't cause any issues.

src/libslic3r/GCode/GCodeWriter.hpp

@@ -200,7 +200,8 @@ public:
     }
 
     void emit_string(const std::string_view s) {
-        strncpy(ptr_err.ptr, s.data(), s.size());
+        // Be aware that std::string_view::data() returns a pointer to a buffer that is not necessarily null-terminated.
+        memcpy(ptr_err.ptr, s.data(), s.size());
         ptr_err.ptr += s.size();
     }