adapt to the upstream changes of AbstractInterpreter interface

[aviatesk]

This shows how Cthulhu can be updated based on JuliaLang/julia#43994.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 40.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.97%. Comparing base (00415a4) to head (b99b283).
⚠️ Report is 373 commits behind head on master.

Files with missing lines	Patch %	Lines
src/interpreter.jl	40.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #264      +/-   ##
==========================================
- Coverage   56.23%   55.97%   -0.27%     
==========================================
  Files           7        7              
  Lines        1115     1122       +7     
==========================================
+ Hits          627      628       +1     
- Misses        488      494       +6     

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