Set back default target of Makefile

[lukland]

Change Summary

Uncomment Makefile first line to be compliant with the docs/contributing.md

Related issue number

Fixes #11996

Checklist

• The pull request title is a good summary of the changes - it will be used in the changelog
• Unit tests for the changes exist
• Tests pass on CI
• Documentation reflects the changes where applicable
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

Selected Reviewer: @DouweM

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.

[codspeed-hq]

CodSpeed Performance Report

Merging #12015 will not alter performance

_{Comparing lukland:fix/contributing-doc-make-target (95531ae) with main (188dc9a)}

Summary

✅ 46 untouched benchmarks

[lukland]

Very small change to be compliant with the documentation, please review

[DouweM]

@lukland Thanks, I had noticed this too but shamefully never fixed it. @Viicos Makes sense to you?

[Viicos]

Thanks @lukland, makes sense!