[CI] Don't run on PRs from forks a job which requires accessing a secret

[giordano]

Also, fix name of input to codecov steps.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.45%. Comparing base (6e2554c) to head (36bdcc5).
Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #661      +/-   ##
==========================================
+ Coverage   72.84%   73.45%   +0.60%     
==========================================
  Files          24       24              
  Lines        3300     3326      +26     
==========================================
+ Hits         2404     2443      +39     
+ Misses        896      883      -13     

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[maleadt]

The alternative is using a pull-request-target rule which does have access to the secret. But I guess this is fine for now.