fix: correct the minimum help output

[snitin315]

What kind of change does this PR introduce?
bug fix

Did you add tests for your changes?
Yes.

If relevant, did you update the documentation?
Yes.
Summary

Don't show multiple --extends in the help output.

Does this PR introduce a breaking change?
No

Other information
No

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (aed6220) 90.89% compared to head (8e7e2d2) 90.89%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4057   +/-   ##
=======================================
  Coverage   90.89%   90.89%           
=======================================
  Files          22       22           
  Lines        1692     1692           
  Branches      488      488           
=======================================
  Hits         1538     1538           
  Misses        154      154           

Files	Coverage Δ
packages/webpack-cli/src/webpack-cli.ts	92.63% <ø> (ø)

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update aed6220...8e7e2d2. Read the comment docs.

[alexander-akait]

Thank you