fix: relax time constraint in block exec test

[jacobowitz]

CI being slow made the blocking exec test fail occassionally

This PR relaxes the asserted execution time constraint a bit. Its a magic number, but I think assuming that it should take less than 2 times the expected time should be fair

[codecov]

Codecov Report

Merging #4653 (c37f226) into master (73718c9) will decrease coverage by 1.14%.
The diff coverage is 94.44%.

@@            Coverage Diff             @@
##           master    #4653      +/-   ##
==========================================
- Coverage   87.46%   86.31%   -1.15%     
==========================================
  Files         117      117              
  Lines        8526     8536      +10     
==========================================
- Hits         7457     7368      -89     
- Misses       1069     1168      +99     

Flag	Coverage Δ
jina	86.31% <94.44%> (-1.08%)	⬇️

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Impacted Files	Coverage Δ
jina/serve/executors/decorators.py	96.96% <0.00%> (-1.52%)	⬇️
jina/serve/runtimes/monitoring.py	100.00% <ø> (ø)
jina/__init__.py	67.46% <100.00%> (ø)
jina/serve/executors/__init__.py	86.50% <100.00%> (+0.16%)	⬆️
jina/serve/networking.py	85.31% <100.00%> (-1.32%)	⬇️
jina/serve/runtimes/gateway/request_handling.py	95.71% <100.00%> (+0.12%)	⬆️
jina/serve/runtimes/head/__init__.py	93.10% <100.00%> (+0.19%)	⬆️
jina/serve/runtimes/worker/__init__.py	94.28% <100.00%> (+0.16%)	⬆️
jina/jaml/parsers/flow/v1.py	45.61% <0.00%> (-52.64%)	⬇️
jina/jaml/parsers/__init__.py	75.60% <0.00%> (-17.08%)	⬇️
... and 19 more

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