fix: false positive watch warning

[alexander-akait]

What kind of change does this PR introduce?

bugfix

Did you add tests for your changes?

Yes

If relevant, did you update the documentation?

No need

Summary

fixes #3778

Does this PR introduce a breaking change?

No, but now we just print a warning about using watch with dev server, but also we avoid extra loop, so our startup time will be faster

Other information

[codecov]

Codecov Report

Merging #3783 (f72d885) into master (8027f71) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3783   +/-   ##
=======================================
  Coverage   91.62%   91.62%           
=======================================
  Files          22       22           
  Lines        1624     1624           
  Branches      463      462    -1     
=======================================
  Hits         1488     1488           
  Misses        136      136           

Impacted Files	Coverage Δ
packages/serve/src/index.ts	79.46% <100.00%> (ø)
packages/webpack-cli/src/webpack-cli.ts	93.02% <100.00%> (ø)

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