Fixed mypy job

[s3rius]

Fixed mypy issue first appeared in #214.

[codecov-commenter]

Codecov Report

Merging #215 (4e7ec54) into develop (e66f3aa) will increase coverage by 5.65%.
Report is 132 commits behind head on develop.
The diff coverage is 73.28%.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

@@             Coverage Diff             @@
##           develop     #215      +/-   ##
===========================================
+ Coverage    67.62%   73.27%   +5.65%     
===========================================
  Files           37       51      +14     
  Lines          942     1553     +611     
===========================================
+ Hits           637     1138     +501     
- Misses         305      415     +110     

Files	Coverage Δ
taskiq/__init__.py	100.00% <100.00%> (ø)
taskiq/abc/formatter.py	100.00% <100.00%> (ø)
taskiq/abc/middleware.py	100.00% <ø> (ø)
taskiq/abc/result_backend.py	100.00% <ø> (ø)
taskiq/abc/schedule_source.py	100.00% <100.00%> (ø)
taskiq/abc/serializer.py	100.00% <100.00%> (ø)
taskiq/acks.py	100.00% <100.00%> (ø)
taskiq/api/__init__.py	100.00% <100.00%> (ø)
taskiq/cli/common_args.py	100.00% <100.00%> (ø)
taskiq/cli/watcher.py	0.00% <ø> (ø)
... and 37 more

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more