fix num_workers for Windows example

[Borda]

What does this PR do?

it was broken already for a while but somehow it has not appeared till yesterday after some other libs update
the very same fix I have done already in #5365

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[carmocca]

shouldn't this target master instead of release?

[codecov]

Codecov Report

Merging #5375 (21c0484) into release/1.2-dev (3c6e06b) will increase coverage by 4%.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           release/1.2-dev   #5375    +/-   ##
================================================
+ Coverage               89%     93%    +4%     
================================================
  Files                  146     146            
  Lines                10361   10361            
================================================
+ Hits                  9220    9597   +377     
+ Misses                1141     764   -377