Fix regression on winc when flashing pem certificates

[alessio-perugini]

Fixed a regression in the winc flasher when trying to upload .pem files

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 6.63%. Comparing base (3b99ab6) to head (e4b472c).
⚠️ Report is 69 commits behind head on main.

Files with missing lines	Patch %	Lines
flasher/winc.go	0.00%	8 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main    #177      +/-   ##
========================================
- Coverage   6.66%   6.63%   -0.03%     
========================================
  Files         24      24              
  Lines       2146    2154       +8     
========================================
  Hits         143     143              
- Misses      1945    1953       +8     
  Partials      58      58              

Flag	Coverage Δ
unit	6.63% <0.00%> (-0.03%)	⬇️

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[umbynos]

Indeed it works on a MKR1000