Only postpone setup script if --num-procs is greater than 1

[hoxbro]

See #6913 (comment)

There is no need to postpone the setup script if we do not run with multiprocessing.

[codecov]

Codecov Report

Attention: Patch coverage is 53.84615% with 12 lines in your changes missing coverage. Please review.

Project coverage is 71.78%. Comparing base (d4f7d68) to head (d340abf).

Files with missing lines	Patch %	Lines
panel/command/serve.py	0.00%	11 Missing ⚠️
panel/io/server.py	50.00%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (d4f7d68) and HEAD (d340abf). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (d4f7d68)	HEAD (d340abf)
	8	7

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #7289       +/-   ##
===========================================
- Coverage   82.18%   71.78%   -10.40%     
===========================================
  Files         337      336        -1     
  Lines       50380    50393       +13     
===========================================
- Hits        41405    36176     -5229     
- Misses       8975    14217     +5242     

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