Fix naming of system-data partitions

[jawn-smith]

This was causing an issue with expanding the filesystems on some core images.

[codecov]

Codecov Report

Merging #26 (4b4879d) into main (10b654d) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #26   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            8         8           
  Lines          979       984    +5     
=========================================
+ Hits           979       984    +5     

Impacted Files	Coverage Δ
internal/statemachine/helper.go	100.00% <100.00%> (ø)

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[sil2100]

Oh man, I remember this part from the Python part indeed. There was much code to rewrite so it doesn't surprise me that we missed something! Thanks for catching it.