There is no application set to open the document “Commit Message.sublime-settings”.

There is no application set to open the document “Commit Message.sublime-settings”.

You’d need to specify an editor in preferences or associate the *.sublime-settings extension to the editor of your choice in order to make it work.
SM didn’t find ST and you seem not to have an editor being set in preferences. Therefore SM tries to open the file with the default application associated with the file extension, which is not set, too.