Reduce GOGC in fuzz tests

[masih]

Investigate false negative fuzz test failures due to hitting memory limit by reverting GOGC back to default 100.

Fixes #666

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.26%. Comparing base (46a498f) to head (8d58db6).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #667      +/-   ##
==========================================
- Coverage   76.43%   76.26%   -0.17%     
==========================================
  Files          65       65              
  Lines        5393     5393              
==========================================
- Hits         4122     4113       -9     
- Misses        873      878       +5     
- Partials      398      402       +4     

see 5 files with indirect coverage changes

[masih]

Repeated fuzzing 3 times with the changes here and the time it take for the fuzzing to run is more or less the same as the time it takes on main.

All three attempts succeeded.