tmp/ folder not in .gitignore file

[dahlo]

Hi, we noticed that the tmp/ folder is not included in the .gitignore file. Any files in tmp/ will be added to a git repo, which in our case resulted in a user name and password being committed to the repo. See issue in admin-plugin, https://github.com/getgrav/grav-plugin-admin/issues/2311#issue-1336538716

An easy fix would be to include tmp/ in the .gitignore file.