Improve test coverage in lift.go

[BooleanCat]

Please provide a brief description of the change.

Improve test coverage in lift.go

Which issue does this change relate to?

N/A.

Contribution checklist.

• [x] I have read and understood the CONTRIBUTING guidelines
• [x] My code is formatted (make check)
• [x] I have run tests (make test)
• [x] All commits in my PR conform to the commit hygiene section
• [x] I have added relevant tests
• [x] I have not added any dependencies

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: +1.59% :tada:

Comparison is base (619dbc8) 98.40% compared to head (498d357) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #51 +/- ## =========================================== + Coverage 98.40% 100.00% +1.59% =========================================== Files 19 19 Lines 376 376 =========================================== + Hits 370 376 +6 + Misses 4 0 -4 + Partials 2 0 -2 ``` [see 1 file with indirect coverage changes](https://app.codecov.io/gh/BooleanCat/go-functional/pull/51/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tom+Godkin)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.