Global warming doesn't come from heat from the ground, but from the atmosphere absorbing extra heat from the sun due to the increased amount of CO2 in it. If this geothermal energy generates enough power so we burn less fossil fuels put less CO2 into the atmosphere, it will slow global warming. The amount of heat we'd get from the ground would be comparable to the amount of heat we get from burning fossil fuels, and both would be negligible compared to the amount of additional heat we get from the sun.
Surely it would have to increase global warming unless there were effects such as a nuclear winter caused by a sudden uncontrolled release of the heat.
If you consider that that heat is stored underground where it doesn't affect weather patterns, then moving it to the surface is bound to involve the use of energy to move it and that energy will contribute to global warming as well as the heat released by the whole project.
My understanding is that it can't really affect it. To the extent we extract heat beyond what the greenhouse effect can warm the earth to, it will radiate out into space. The only real way to heat up the planet long-term is to prevent heat from radiating out by increasing greenhouse gasses.