Fix UTM loader to skip non-disks

[Schamper]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 75.17%. Comparing base (ff47f07) to head (4014ea9).

Files	Patch %	Lines
dissect/target/loaders/utm.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #769      +/-   ##
==========================================
- Coverage   75.17%   75.17%   -0.01%     
==========================================
  Files         295      295              
  Lines       25315    25317       +2     
==========================================
+ Hits        19031    19032       +1     
- Misses       6284     6285       +1     

Flag	Coverage Δ
unittests	75.17% <50.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

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