Is your branch master or main?
It might be silly in the future but as for October 2020 just keep in mind that the default GitHub branch has been renamed from master to main (source)
So if you are copypasting actions from elsewhere, make sure that you are targeting the correct branch (for new repos this means most of the time to replace master with main in the .yml workflow files).
If you are targeting the wrong branch, the name of the action will appear on GitHub but no actions will actually run.