chore(deps): bump openpyxl from 3.1.2 to 3.1.5 in /backend

Bumps [openpyxl](https://openpyxl.readthedocs.io

) from 3.1.2 to 3.1.5.

---
updated-dependencies:
- dependency-name: openpyxl
  dependency-type: direct:production
  update-type: version-update:semver-patch
...
Signed-off-by: dependabot[bot] <support@github.com>

backend/requirements.txt

@@ -44,7 +44,7 @@ unstructured==0.14.0
 Markdown==3.6
 pypandoc==1.13
 pandas==2.2.2
-openpyxl==3.1.2
+openpyxl==3.1.5
 pyxlsb==1.0.10
 xlrd==2.0.1
 validators==0.28.1