Bug 1645393 - Install python3 development files in build docker images. r=firefox-build-system-reviewers,rstewart

It's required to properly setup psutil in the python3 virtualenv, and
psutil is required for build resources tracking by mach.

It's not clear to me why this hasn't been a problem since `mach build`
switched to python3, though. ¯\_(ツ)_/¯

Differential Revision: https://phabricator.services.mozilla.com/D80343

taskcluster/docker/android-build/Dockerfile

@@ -28,6 +28,7 @@ RUN apt-get update && \
       python-pip \
       python-setuptools \
       python-virtualenv \
+      python3-dev \
       rsync \
       screen \
       sudo \

taskcluster/docker/debian-build/Dockerfile

@@ -62,6 +62,7 @@ RUN apt-get update && \
       python-pip \
       python-setuptools \
       python-virtualenv \
+      python3-dev \
       rsync \
       screen \
       tar \