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)

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[alexander-akait]

Thank you