add dart 2.18

[QuintenQVD0]

Description

Add dart 2.18 what has at it base dart:2.18.6 as dart:2.18 is 2.18.0 and that is not the latest 2.18 and I think this will be the latest 2.18 as there are already 2.19 beta tags

All Submissions:

• [x] Have you ensured there aren't other open Pull Requests for the same update or change?
• [x] Have you created a new branch for your changes and PR from that branch and not from your master branch?

New Image Submissions:

1. [x] Have you added your image to the Github workflows?
2. [x] Have you updated the README list to contain your new image?