executors: make Zig executor work with 0.8.1

[quantum5]

This will help with #920.

Do not merge until we figured out what to do with past submissions.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 52.26%. Comparing base (8072c5e) to head (45fe294).
Report is 361 commits behind head on master.

Files with missing lines	Patch %	Lines
dmoj/executors/ZIG.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #920       +/-   ##
===========================================
- Coverage   86.22%   52.26%   -33.97%     
===========================================
  Files         138      138               
  Lines        4633     4628        -5     
===========================================
- Hits         3995     2419     -1576     
- Misses        638     2209     +1571     

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