More u-root build tests

[hugelgupf]

No description provided.

[codecov]

Codecov Report

Attention: 11 lines in your changes are missing coverage. Please review.

Comparison is base (44f9530) 63.06% compared to head (8906270) 65.75%.

Files	Patch %	Lines
uroot/uroot.go	70.00%	6 Missing ⚠️
uroot/initramfs/test/ramfs.go	42.85%	2 Missing and 2 partials ⚠️
uroot/initramfs/files.go	95.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #7      +/-   ##
==========================================
+ Coverage   63.06%   65.75%   +2.69%     
==========================================
  Files          21       21              
  Lines        1259     1282      +23     
==========================================
+ Hits          794      843      +49     
+ Misses        342      325      -17     
+ Partials      123      114       -9     

Flag	Coverage Δ
ubuntu-latest-unit	65.75% <76.59%> (+2.69%)	⬆️

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