arch: fix json erro with no card

[mloubout]

Makes cache line size detection error when there is no GPU (json.loads line 302 errors with empty lines)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.99%. Comparing base (512d7f3) to head (de655df).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2620   +/-   ##
=======================================
  Coverage   91.99%   91.99%           
=======================================
  Files         245      245           
  Lines       48495    48495           
  Branches     4261     4261           
=======================================
  Hits        44612    44612           
  Misses       3202     3202           
  Partials      681      681           

Flag	Coverage Δ
pytest-gpu-aomp-amdgpuX	72.55% <0.00%> (ø)
pytest-gpu-nvc-nvidiaX	73.61% <0.00%> (ø)

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