fix: Use proper chain ID for signTypedData example

[FrederikBolding]

When writing the signTypedData example I had based the code on some example code that hardcoded the chain ID. Instead we should use the current chain ID, so we can test the Snap on any chain.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.75%. Comparing base (493eedc) to head (8fc722a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3013   +/-   ##
=======================================
  Coverage   94.75%   94.75%           
=======================================
  Files         497      497           
  Lines       10896    10896           
  Branches     1674     1674           
=======================================
  Hits        10325    10325           
  Misses        571      571           

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