Changed help message of --num-worker-threads flag

[danielsagi]

Description

Following #433 added a minor change in the help message of the flag.

Contribution checklist

• [x] I have read the Contributing Guidelines.
• [ ] The commits refer to an active issue in the repository.
• [x] I have added automated testing to cover this case.

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[codecov[bot]]

Codecov Report

Merging #501 (3b7c005) into main (2a70206) will increase coverage by 0.72%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #501      +/-   ##
==========================================
+ Coverage   64.55%   65.28%   +0.72%     
==========================================
  Files          46       44       -2     
  Lines        2531     2457      -74     
==========================================
- Hits         1634     1604      -30     
+ Misses        897      853      -44     

Impacted Files	Coverage Δ
kube_hunter/conf/logging.py	100.00% <ø> (ø)
kube_hunter/modules/hunting/__init__.py	100.00% <ø> (ø)
kube_hunter/conf/__init__.py	97.05% <100.00%> (+0.08%)	:arrow_up:
kube_hunter/conf/parser.py	81.81% <100.00%> (+0.56%)	:arrow_up:
kube_hunter/core/events/handler.py	86.66% <100.00%> (-0.53%)	:arrow_down:

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