fix: assert_that_code does not highlight diffs in failures

[haraldmaida]

When asserting that code panics using the macro assert_that_code! or function assert_that_code() the differences in the panic message are not highlighted on failed assertion.

The function assert_that_code has been fixed to set the diff format according the configured mode.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.07%. Comparing base (8db9340) to head (fc72abf).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #30      +/-   ##
==========================================
+ Coverage   94.05%   94.07%   +0.02%     
==========================================
  Files          24       24              
  Lines        2338     2347       +9     
  Branches     2338     2347       +9     
==========================================
+ Hits         2199     2208       +9     
  Misses        133      133              
  Partials        6        6              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.