fix: prevent unintended mutation of latestHeader.Number in ParentChainIsUsingEIP7623

[ruslan0012]

The Sub() method on *big.Int modifies the receiver in place. The old code was mutating latestHeader.Number that was passed from the caller, which could lead to incorrect block number being used after the function returns.

Changed from:
latestHeader.Number.Sub(latestHeader.Number, big.NewInt(5))

To:
new(big.Int).Sub(latestHeader.Number, big.NewInt(5))

This matches the pattern used elsewhere in the codebase (e.g. challenge_manager.go:220).

[eljobe]

Nice catch. This isn't currently causing any problems, because the only caller of this method in production code doesn't go on to use the latestHeader.Number later in the code. But, if the code were changed to start reading it, this would, indeed be quite surprising.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.24%. Comparing base (9e434ee) to head (eb49c49).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4116       +/-   ##
===========================================
+ Coverage   33.05%   57.24%   +24.19%     
===========================================
  Files         459      459               
  Lines       55830    55830               
===========================================
+ Hits        18453    31959    +13506     
+ Misses      34159    19072    -15087     
- Partials     3218     4799     +1581     

[pmikolajczyk41]

@ruslan0012 please add a changelog fragment

[ruslan0012]

done, thanks

[joshuacolvin0]

LGTM