fix: set GSA fix_sats_prn from 12 to 18

[elpiel]

Fixes #115

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (196199e) 77.62% compared to head (b05920b) 77.62%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #116   +/-   ##
=======================================
  Coverage   77.62%   77.62%           
=======================================
  Files          34       34           
  Lines        1247     1247           
=======================================
  Hits          968      968           
  Misses        279      279           

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[elpiel]

This PR is wrong, maybe the parsing or the LC76G sentences documentation is wrong as it also mentions a max if 12 prns