Bump lightgbm in /backend in the pip group across 1 directory

Bumps the pip group with 1 update in the /backend directory: [lightgbm](https://github.com/microsoft/LightGBM).


Updates `lightgbm` from 4.5.0 to 4.6.0
- [Release notes](https://github.com/microsoft/LightGBM/releases)
- [Commits](microsoft/LightGBM@v4.5.0...v4.6.0)

---
updated-dependencies:
- dependency-name: lightgbm
  dependency-type: direct:production
  dependency-group: pip
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

backend/requirements.txt

@@ -11,7 +11,7 @@ diffusers==0.32.2
 numpy==1.26.4
 joblib==1.4.2
 xgboost==2.1.3
-lightgbm==4.5.0
+lightgbm==4.6.0
 scikit-learn==1.6.1
 rapidfuzz==3.12.1
 Levenshtein==0.26.1