TestKit backend: fix missing Python build dependency

Author: robsdedude

testkit/Dockerfile

@@ -25,7 +25,7 @@ RUN apt-get update && \
     apt-get install -y --no-install-recommends \
         make build-essential libssl-dev zlib1g-dev libbz2-dev libreadline-dev \
         libsqlite3-dev wget curl llvm libncurses5-dev xz-utils tk-dev \
-        libxml2-dev libxmlsec1-dev libffi-dev \
+        libxml2-dev libxmlsec1-dev libffi-dev liblzma-dev \
         ca-certificates && \
     apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*