Add width to prevent image overflow in trial flow first step

What does this MR do and why?

Fix image size in the first step of the trial flow to prevent overflow.

Note: This visual issue only happens on Google Chrome/Chromium based browser.

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Use Google Chrome
2. Login and go to http://localhost:3000/-/trials/new

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.