test: add gitea pypi index url

Dockerfile

@@ -12,7 +12,9 @@ WORKDIR /app
 # Install only runtime dependencies needed for bibapi and requests
 # This avoids installing Playwright browsers which are huge
 COPY requirements.txt ./
-RUN pip install --no-cache-dir -r requirements.txt && \
+RUN pip install --no-cache-dir \
+    --extra-index-url https://git.theprivateserver.de/api/packages/PHB/pypi/simple/ \
+    -r requirements.txt && \
     # Clean up pip cache
     rm -rf /root/.cache/pip