Organizing the is_scalar_field function check logic

[aniaan]

When I read this code of the is_scalar_field function, the logic here is a little difficult to read, here take not + not, I think here can reorganize the code to make it more clear and understandable

[codecov]

Codecov Report

Merging #2307 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #2307   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          240       240           
  Lines         7101      7101           
=========================================
  Hits          7101      7101           

Impacted Files	Coverage Δ
fastapi/dependencies/utils.py	100.00% <100.00%> (ø)

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[github-actions]

📝 Docs preview for commit 187ee30 at: https://5fa50947b81279aba641f3cf--fastapi.netlify.app