Check the k3s-root sha256sum

[manuelbuil]

Proposed Changes

This PR adds a sha256sum check to verify that the tarball was not tampered

Types of Changes

Security improvement

Verification

Testing

Linked Issues

#13886

User-Facing Change

Further Comments

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 22.32%. Comparing base (f1deb4e) to head (6495725).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13888      +/-   ##
==========================================
- Coverage   22.38%   22.32%   -0.07%     
==========================================
  Files         193      193              
  Lines       15631    15631              
==========================================
- Hits         3499     3489      -10     
- Misses      11650    11662      +12     
+ Partials      482      480       -2     

Flag	Coverage Δ
unittests	22.32% <ø> (-0.07%)	⬇️

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