Change character limit from 200 to 300 for actions in report

[kerryalyons]

Feedback:

Only 200 characters is not enough to give full and well-rounded feedback on the reasons for a particular action here.

I want to tell them to use the DfE design histories. But they already have a Heroku one and I want to make sure I acknowledge that exists and flag things they need to do to make what they have more accessible and searchable. I can't do that in 200 characters.

This page in the service:

https://service-assessments.education.gov.uk/assess/report-section-actions-add/30/13