Make extract-source job run faster

Currently in MariaDB builds the extract-source job takes 8-10 minutes to complete. The log output does not have timestamps so hard to say why it is slow.

Could it be related to git repository size? Would it make sense to try to clone the git repository with git clone --shallow-since=3m --recurse-submodules --shallow-submodules so it does not download everything? Or gbp clone --depth=1 if it uses gbp.

Ideas and suggestions how to make extract-source faster are welcome!