[bugfix] Fix config error when authorization_header is not set in the httpjson handler

[ekouts]

Reframe would raise a config error when authorization_header is not set in the httpjson handler.

ERROR: failed to load configuration: httpjson: 'authorization_header' has the wrong signature: it must be 'authorization_header()'

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.90%. Comparing base (307a37c) to head (1cfbe2f).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3711   +/-   ##
=======================================
  Coverage   91.90%   91.90%           
=======================================
  Files          62       62           
  Lines       13782    13782           
=======================================
  Hits        12667    12667           
  Misses       1115     1115           

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[vkarak]

Can you describe more precisely when it fails? With a config snippet maybe? Afaiu, the authorization_header breaks existing httpsjson handler definitions.