CompatHelper: bump compat for "FFTW" to "1.2"

[github-actions]

This pull request changes the compat entry for the FFTW package from < 1.2 to < 1.2, 1.2.

This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov]

Codecov Report

Merging #56 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #56   +/-   ##
=======================================
  Coverage   98.62%   98.62%           
=======================================
  Files           6        6           
  Lines         510      510           
=======================================
  Hits          503      503           
  Misses          7        7

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