fix: use 3.5 version of get-pip.py

Author: Rui Wang Napieralski

tests/data/multimodel/container/Dockerfile

@@ -15,7 +15,7 @@ RUN apt-get update && \
     curl \
     vim \
     && rm -rf /var/lib/apt/lists/* \
-    && curl -O https://bootstrap.pypa.io/get-pip.py \
+    && curl -O https://bootstrap.pypa.io/3.5/get-pip.py \
     && python3 get-pip.py
 
 RUN update-alternatives --install /usr/bin/python python /usr/bin/python3 1