fix: lowercase field type check in internal field transform

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (55806a0) 91.21% compared to head (9860b55) 82.07%.

:exclamation: Current head 9860b55 differs from pull request most recent head da50108. Consider uploading reports for the commit da50108 to get more accurate results

Files	Patch %	Lines
.../catalog_view_api/service/ConceptsMapperService.kt	66.66%	0 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #45 +/- ## ============================================ - Coverage 91.21% 82.07% -9.14% + Complexity 112 64 -48 ============================================ Files 19 19 Lines 535 530 -5 Branches 70 71 +1 ============================================ - Hits 488 435 -53 - Misses 14 65 +51 + Partials 33 30 -3 ```

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