chore: update lerna to v6

[snitin315]

What kind of change does this PR introduce?
deps update

Did you add tests for your changes?
No.

If relevant, did you update the documentation?

Summary

Fix #3448

Does this PR introduce a breaking change?
No

Other information
No

[codecov]

Codecov Report

Merging #3457 (d1d51c3) into next (0f7da89) will increase coverage by 20.76%.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff             @@
##             next    #3457       +/-   ##
===========================================
+ Coverage   70.53%   91.30%   +20.76%     
===========================================
  Files          21       22        +1     
  Lines        1585     1587        +2     
  Branches      447      447               
===========================================
+ Hits         1118     1449      +331     
+ Misses        467      138      -329     

Impacted Files	Coverage Δ
packages/generators/addon-template/package.json.js	100.00% <0.00%> (ø)
packages/serve/src/index.ts	78.94% <0.00%> (+4.38%)	⬆️
packages/configtest/src/index.ts	96.00% <0.00%> (+12.00%)	⬆️
packages/webpack-cli/src/plugins/CLIPlugin.ts	100.00% <0.00%> (+14.54%)	⬆️
packages/webpack-cli/src/webpack-cli.ts	92.69% <0.00%> (+18.06%)	⬆️
packages/webpack-cli/src/bootstrap.ts	100.00% <0.00%> (+25.00%)	⬆️
packages/generators/src/plugin-generator.ts	100.00% <0.00%> (+28.57%)	⬆️
packages/generators/src/utils/scaffold-utils.ts	100.00% <0.00%> (+37.50%)	⬆️
packages/generators/src/loader-generator.ts	91.66% <0.00%> (+41.66%)	⬆️
packages/generators/src/index.ts	86.36% <0.00%> (+43.18%)	⬆️
... and 3 more

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[alexander-akait]

@snitin315 Any critical breaking changes for us?

[snitin315]

@alexander-akait No, we are good. In v5 they dropped node 12 support and in v6 they updated some defaults.

[alexander-akait]

@snitin315 Feel free to emrge when CI will be green 👍