new icon: testrail (plain, plain-wordmark)

[artifexrefercio]

Double check these details before you open a PR

• [x] PR does not match another non-stale PR currently opened
• [x] PR name matches the format new icon: Icon name (versions separated by comma). More details here
• [x] PR's base is the develop branch.
• [x] Your icons are inside a folder as seen here
• [x] SVG matches the standards laid out here
• [x] A new object is added in the devicon.json file at the correct alphabetic position as seen here

This PR closes #2403

Link to prove your SVG is correct and up-to-date.

https://www.testrail.com/ - the plain-wordmark is used as logo menu

[Snailedlt]

@artifexrefercio let us know if you want any help :)

[github-actions[bot]]

Hi!

I'm the check-bot and we have some issues with your PR:

Error found regarding filenames:
- This path doesn't exist: '/home/runner/work/devicon/devicon/icons/testrail/testrail-plain.svg'

Error checking SVGs: no SVGs to check. Might be caused by above issues.

Check our CONTRIBUTING guide for more details regarding these errors.

Please address these issues. When you update this PR, I will check your SVGs again.

Thanks for your help, SVG-Checker Bot :smile: