Fixes `for` specific error message.

[esdrubal]

The added test case was emitting a wrong/confusing error message, because a for loop only gets type-checked in its desugared form, as a while loop.

The error message was A while loop's loop body cannot implicitly return a value. Try assigning it to a mutable variable declared outside of the loop instead.

Corrected to: A for loop's loop body cannot implicitly return a value. Try assigning it to a mutable variable declared outside of the loop instead.

Fixes #6395

Description

Checklist

• [ ] I have linked to any relevant issues.
• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] I have updated the documentation where relevant (API docs, the reference, and the Sway book).
  • [ ] If my change requires substantial documentation changes, I have requested support from the DevRel team
• [ ] I have added tests that prove my fix is effective or that my feature works.
• [ ] I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• [ ] I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• [ ] I have requested a review from the relevant team or maintainers.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #6758 will not alter performance

_{Comparing esdrubal/6395 (f4d9fba) with master (64d1c6e)}

Summary

✅ 22 untouched benchmarks