test(iam): fix tests crashing in case of get api-key failure

[estellesoulard]

Following this failed job: https://github.com/scaleway/scaleway-cli/actions/runs/18701945888/job/53332405971#step:4:62

• fix panic happening outside of test function context

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.33%. Comparing base (3ec89ce) to head (998a367).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5075   +/-   ##
=======================================
  Coverage   56.33%   56.33%           
=======================================
  Files         307      307           
  Lines       78498    78498           
=======================================
  Hits        44219    44219           
  Misses      32845    32845           
  Partials     1434     1434           

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