Remove Slack orb usage from Win job on CircleCI

[dmitryduev]

Description

...because Windows is currently not supported by the Slack orb, see CircleCI-Public/slack-orb#282.

Testing

How was this PR tested?

Checklist

• Include reference to internal ticket "Fixes WB-NNNN" (and github issue "Fixes #NNNN" if applicable)

[codecov]

Codecov Report

Merging #4171 (868fbc0) into master (4c87b36) will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4171      +/-   ##
==========================================
+ Coverage   82.66%   82.72%   +0.05%     
==========================================
  Files         256      256              
  Lines       32533    32533              
==========================================
+ Hits        26894    26912      +18     
+ Misses       5639     5621      -18     

Flag	Coverage Δ
functest	55.01% <ø> (+0.03%)	⬆️
unittest	73.50% <ø> (+0.07%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
wandb/sdk/wandb_login.py	94.54% <0.00%> (-0.61%)	⬇️
wandb/sdk/lib/git.py	79.01% <0.00%> (ø)
wandb/sdk/wandb_setup.py	88.94% <0.00%> (+0.50%)	⬆️
wandb/sdk/internal/internal_api.py	86.98% <0.00%> (+0.90%)	⬆️
wandb/filesync/step_prepare.py	94.93% <0.00%> (+1.26%)	⬆️
wandb/integration/tensorboard/monkeypatch.py	92.59% <0.00%> (+2.46%)	⬆️
wandb/sdk/internal/meta.py	90.79% <0.00%> (+3.06%)	⬆️
wandb/sdk/internal/artifacts.py	87.50% <0.00%> (+3.12%)	⬆️