build(deps): bump einops from 0.8.0 to 0.8.1 in /backend

Bumps [einops](https://github.com/arogozhnikov/einops) from 0.8.0 to 0.8.1.
- [Release notes](https://github.com/arogozhnikov/einops/releases)
- [Commits](https://github.com/arogozhnikov/einops/compare/v0.8.0...v0.8.1)

---
updated-dependencies:
- dependency-name: einops
  dependency-version: 0.8.1
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

backend/requirements.txt

@@ -55,7 +55,7 @@ elasticsearch==8.17.1
 transformers
 sentence-transformers==3.3.1
 colbert-ai==0.2.21
-einops==0.8.0
+einops==0.8.1
 
 
 ftfy==6.2.3