Sanitize ExUnit formatters against invalid UTF-8

[kidq330]

• Describe here the reasons behind the pull request.
  This is a fix for a crash in ExUnit that I came across while debugging missing logs for a test suite that turned out to hit the already-fixed diff crashing the formatter: 0055f2fe53. Nevertheless it is reproducible as shown in this minimal mix project. I believe ExUnit fails on Ecto exception error #11108 might be related

• Make sure you have read the CONTRIBUTING.md file.
  ✅

• Make sure any relevant documentation and tests have been added/updated.
  N/A

• Do not submit Draft pull requests unless previously asked/agreed.
  N/A

• AI assistance
  The tests were AI generated, I applied the fixes

[josevalim]

I propose for us to first change only the cli formatter to escape logs indeed. Can you please amend accordingly? For the tests, we have an integration suite where we already check for capture logs, so we can add a single new test there. Thanks!