Disable pip cache when installing Mercurial

infra/dockerfile.commit_retrieval

@@ -3,7 +3,7 @@ FROM mozilla/bugbug-base:latest
 # Mercurial need Python2 :(
 RUN apt-get update && apt-get install -y python-pip && rm -rf /var/lib/apt/lists/*
 
-RUN python2 -m pip install mercurial==4.8
+RUN python2 -m pip install --disable-pip-version-check --no-cache-dir mercurial==4.8
 
 # Robustcheckout setup
 RUN hg clone -r 6cd994e30bb1 https://hg.mozilla.org/hgcustom/version-control-tools /version-control-tools/