docker,worker: install pyelftools

docker,worker: install pyelftools

Without it, errors may appear:

WARNING: Makefile 'package/feeds/telephony/freeswitch/Makefile' has a dependency on 'libpcre', which does not exist
make[2]: Entering directory '/builder/shared-workdir/build/scripts/config'
make[2]: 'conf' is up to date.
make[2]: Leaving directory '/builder/shared-workdir/build/scripts/config'
Checking 'python3-pyelftools'... failed.
Checking 'python3-dev'... ok.
Checking 'python3-setuptools'... ok.
Checking 'swig'... ok.
u-boot: Please install the Python3 elftools module

Fixes: 3ac7d39bd4c3 ("buildworker,buildmaster: bump Debian to version 12")
Signed-off-by: Paul Spooren <mail@aparcar.org>