The latest round of subpoenas from the congressional committee investigating the Jan. 6 Capitol attack suggests the panel is deepening its probe of how allies of former President Donald Trump urged legislatures in key swing states to subvert the 2020 election. But the subpoenas also shine a spotlight on a leading contender in Pennsylvania’s Republican primary for governor: State Sen. Doug Mastriano. In a letter to Mastriano, the committee demanded documents and testimony regarding his involvement in a plan to send a pro-Trump slate of electors to Congress from Pennsylvania, despite Joe Biden’s…