test: Add test for checkNetworkID

[kuznetsss]

High Level Overview of Change

Add missing test for checkNetworkID() .

Context of Change

API Impact

• Public API: New feature (new methods and/or new fields)
• Public API: Breaking change (in general, breaking changes should only impact the next api_version)
• libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
• Peer protocol change (must be backward compatible or bump the peer protocol version)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.0%. Comparing base (07c64f0) to head (1b17f69).

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #7624   +/-   ##
=======================================
  Coverage     82.0%   82.0%           
=======================================
  Files         1007    1007           
  Lines        76890   76890           
  Branches      8971    8965    -6     
=======================================
  Hits         63050   63050           
  Misses       13831   13831           
  Partials         9       9           

see 6 files with indirect coverage changes

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