Linux build failing due to change in artifacts extension

See: https://nightlies.tbb.torproject.org/nightly-builds/tor-browser-builds/tbb-nightly.2025.06.16/nightly-linux-x86_64/logs/firefox-linux-x86_64.log

18:32.61 Created package: /var/tmp/build/firefox-297b2e99b45a/obj-x86_64-pc-linux-gnu/dist/firefox-140.0a1.en-US.linux-x86_64.tar.xz
Running "pip check" to verify compatibility between the system Python and the "mach" site.
Running "pip check" to verify compatibility between the system Python and the "common" site.
cp: cannot stat 'obj-*/dist/*.tar.bz2': No such file or directory

We are trying to copy a .tar.bz2 file, but now its .tar.xz.