The liberal nonprofit End Citizens United filed a complaint against Tim Sheehy, the frontrunner in Montana’s U.S. Senate GOP primary, alleging he’s missing some details on his personal financial disclosure. Sheehy is running for the chance to unseat Sen. Jon Tester (D-Mont.) in one of this cycle’s most hotly contested Senate races. He’s also incredibly wealthy, with a net worth between $74 million and $260 million based…