Say I create an Open Source project on Github licensed under e.g. LGPL like Qt. As I understand ownership of code, if I wrote a piece of code, I am free to change the license at a later point, as long as I keep a LGPL version of the old code. This could be because I want to further develop it into a solution I want to sell, again like the Qt dual license.
Enter a pull request. Someone commits 10 lines to the LGPL version. Can I no longer change the license, or do I essentially still own the code since it is my repo?