Install 'git' package in the commit_retrieval image

Even though it's only required for the annotate pipeline.

infra/dockerfile.commit_retrieval

@@ -1,7 +1,8 @@
 FROM mozilla/bugbug-base:latest
 
 # Mercurial need Python2 :(
-RUN apt-get update && apt-get install -y python-pip && rm -rf /var/lib/apt/lists/*
+# git is required by the annotate pipeline.
+RUN apt-get update && apt-get install -y python-pip git && rm -rf /var/lib/apt/lists/*
 
 RUN python2 -m pip install --disable-pip-version-check --no-cache-dir mercurial==4.8