support/docker: add python3-magic

It will be needed by check-package to run checks according to the file
type (the same determined by the command 'file').

Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

support/docker/Dockerfile

@@ -39,6 +39,7 @@ RUN apt-get install -y --no-install-recommends \
         openssh-server \
         python3 \
         python3-flake8 \
+        python3-magic \
         python3-nose2 \
         python3-pexpect \
         python3-pytest \