Rigid local systems on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" display="inline" overflow="scroll"><mml:msub><mml:mi mathvariant="double-struck">G</mml:mi><mml:mi>m</mml:mi></mml:msub></mml:math> with finite monodromy