TST Add seed to 2D FFT test in TF

[janden]

This is a bit flaky, so let's fix the seed here.

Should probably be doing this more consistently across the tests, but that's another discussion.

[codecov-commenter]

Codecov Report

Merging #896 (8e1327c) into dev (8e1327c) will not change coverage.
The diff coverage is n/a.

❗ Current head 8e1327c differs from pull request most recent head ce0586b. Consider uploading reports for the commit ce0586b to get more accurate results

@@           Coverage Diff           @@
##              dev     #896   +/-   ##
=======================================
  Coverage   88.14%   88.14%           
=======================================
  Files          64       64           
  Lines        2226     2226           
=======================================
  Hits         1962     1962           
  Misses        264      264           

Flag	Coverage Δ
jenkins_main	88.14% <0.00%> (ø)

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