test(instance): add test for server with scratch storage

[Mia-Cross]

This PR adds a test that creates a server with a scratch volume attached to it.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 1.76%. Comparing base (e42aa63) to head (be8b7d9).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #3510   +/-   ##
======================================
  Coverage    1.76%   1.76%           
======================================
  Files         406     406           
  Lines       44434   44434           
======================================
  Hits          786     786           
  Misses      43561   43561           
  Partials       87      87           

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