fix: Make sure there's enough space for CONSUME1 in fuzzers.

[iphydf]

This change is 

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (50f1b30) 68.13% compared to head (812f931) 68.27%.

Files	Patch %	Lines
toxcore/group_announce_fuzz_test.cc	28.57%	5 Missing ⚠️
testing/fuzzing/fuzz_support.h	77.77%	2 Missing ⚠️
toxcore/forwarding_fuzz_test.cc	0.00%	2 Missing ⚠️
toxcore/DHT_fuzz_test.cc	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2552      +/-   ##
==========================================
+ Coverage   68.13%   68.27%   +0.13%     
==========================================
  Files         118      118              
  Lines       28162    28162              
==========================================
+ Hits        19188    19227      +39     
+ Misses       8974     8935      -39     

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