Fix a typo in JAX gengamma

[Smit-create]

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Fixes #1472

[codecov]

Codecov Report

Merging #1475 (fb57b6e) into main (984ee55) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1475   +/-   ##
=======================================
  Coverage   75.02%   75.02%           
=======================================
  Files         194      194           
  Lines       50099    50099           
  Branches    12096    12096           
=======================================
  Hits        37586    37586           
  Misses      10189    10189           
  Partials     2324     2324           

Impacted Files	Coverage Δ
aesara/link/jax/dispatch/random.py	100.00% <100.00%> (ø)

[brandonwillard]

Thanks again, @Smit-create!