Fix incorrect use of pytest.raises(message=...)

[zejn]

According to pytest-dev/pytest#3974 python-jose was using pytest.raises incorrectly.

[codecov]

Codecov Report

Merging #141 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #141   +/-   ##
=======================================
  Coverage   96.54%   96.54%           
=======================================
  Files          14       14           
  Lines        1071     1071           
=======================================
  Hits         1034     1034           
  Misses         37       37

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