WIP: set locale to fix msggrep warning

I can't reproduce warning from #27 (closed) (msggrep: warning: Locale charset "ANSI_X3.4-1968" is different from) in my development environment. I found the solution here: gitlab-org/gitlab-foss#14983 (comment 4637913)

Maybe these lines are unnecessary:

- apt-get update >/dev/null
- apt-get install -y locales >/dev/null

I see in the job log:

$ apt-get update >/dev/null
$ apt-get install -y locales >/dev/null
debconf: delaying package configuration, since apt-utils is not installed
$ echo "en_US UTF-8" > /etc/locale.gen
$ locale-gen en_US.UTF-8
Generating locales (this might take a while)...
  en_US.UTF-8... done
Generation complete.
$ export LANG=en_US.UTF-8
$ export LANGUAGE=en_US:en
$ export LC_ALL=en_US.UTF-8
$ cd $target_dir

Please review.

Fixes #27 (closed)