Merge pull request #12255 from open-webui/dependabot/pip/backend/dev/pypandoc-1.15

build(deps): bump pypandoc from 1.13 to 1.15 in /backend

backend/requirements.txt

@@ -67,7 +67,7 @@ python-pptx==1.0.0
 unstructured==0.16.17
 nltk==3.9.1
 Markdown==3.7
-pypandoc==1.13
+pypandoc==1.15
 pandas==2.2.3
 openpyxl==3.1.5
 pyxlsb==1.0.10