There is no strings attached to the use of System Workbench for STM32. You can publish your code the way you want, on any platform you like. The licenses that are displayed apply to the tool itself or the firmware code provided by ST (that can only be used on STM32X MCUs) or others, but your code can be licensed on the licensing terms you prefer, as long as your license is only applying to your code (a license that would request licensing all code linked to your code to be licensed similarly may conflicts with the firmware license); however this is only a question fo choice for the licensing you apply to your code, not to constraints of the source code hosting platform.
Hoping this woll clarify things,
PS: Note that this means that GPL may not be appropriate, while Apache will most certainly be. However, as usual, IANAL (I am not a lawyer )