Use NET9 sdk in signing pipeline

[mdaigle]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.64%. Comparing base (b9877f4) to head (23d12d0).
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #3039       +/-   ##
===========================================
- Coverage   92.58%   72.64%   -19.94%     
===========================================
  Files           6      285      +279     
  Lines         310    59171    +58861     
===========================================
+ Hits          287    42987    +42700     
- Misses         23    16184    +16161     

Flag	Coverage Δ
addons	92.58% <ø> (ø)
netcore	75.45% <ø> (?)
netfx	71.02% <ø> (?)

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