LOS ANGELES—Scarlett Johansson, star of the Marvel superhero movie “Black Widow,” sued the Walt Disney Co on Thursday, alleging that the company breached her contract when it offered the movie on streaming at the same time it played in theaters. Disney said there was “no merit” to the lawsuit, saying it had complied with her contract. It added in a statement that the release of the movie on its streaming platform had “significantly enhanced her (Johansson’s) ability to earn additional compensation on top of the $20 million she has received to date.” Johansson’s complaint, filed in Los Angeles Superior Court, argued that the dual release strategy of “Black Widow” had reduced her compensation, which was based partly on box office receipts from what was supposed to be an exclusive run in cinemas. “Black Widow” debuted on July 9 in theaters and for a $30 charge on the Disney+ streaming service. …