Resize Icons on Env Dashbord

[charleyf]

Relevant Ticket or Conversation:

I noticed earlier today that our environments dashboard is showing large icons after changes in the design system [1, 2].

https://dashboard.dev.identitysandbox.gov/env

Before this PR

After this PR

Description of Changes:

This PR resizes the icons on the dashboard page here: https://dashboard.dev.identitysandbox.gov/env.

Note: Searching for image_tag across this repo shows me other potential icon size problems in app/views/service_providers/_service_provider_table_row.erb and app/views/users/index.html.erb, but I can't easily get to those pages locally so I'm deferring that for now.

PR Checklist:

1. [x] Have you linted and tested your code locally prior to submission?
   • [x] Successful make lint
   • [x] Successful make test (6 pending tests, but I doubt that's related to this PR)
2. [x] Have you tagged the appropriate dev(s) for review?
   • [x] Andrew Duthie tagged for review
3. [x] Have you linked to any relevant tickets or conversations?
   • [x] Yes, but it's minimal.

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• Consider using Conventional Comments to ensure that your feedback is clear and actionable.
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