Pin Vega and related dependencies on Dockerfile

Same as iterative/setup-cml#40 & iterative/setup-cml#41 but for our container images.

Dockerfile

@@ -91,7 +91,7 @@ RUN add-apt-repository universe --yes \
  && apt-get clean \
  && rm --recursive --force /var/lib/apt/lists/* \
  && npm config set user 0 \
- && npm install --global canvas vega vega-cli vega-lite
+ && npm install --global canvas@2 vega@5 vega-cli@5 vega-lite@4
 
 # CONFIGURE RUNNER PATH
 ENV RUNNER_PATH=/home/runner