gbp import-orig: how to choose compression (xz)

[Lorenzo <plorenzo@disroot.org>]

Hello mentors,

I want to import a new svn snapshot to update a Debian package,
the salsa git repo is already configured for gbp, so I did

$ gbp import-orig -u1.5+svn38408 ../upstreamsvn/mplayer

upstream/mplayer is a directory with the unpacked svn checkout.
Gbp creates a ../upstreamsvn/mplayer_1.5+svn38408.orig.tar.gz
archieve (not a tar.xz); it also uses tar.gz in the pristine-tar branch.

One problem with the tar.gz is that debian/gbp.conf has
compression = xz
so when I push to salsa the salsa-ci fails because it searches for a
tar.xz archieve

gbp:info: All Orig tarballs 'mplayer_1.5+svn38408.orig.tar.xz' found at '/builds/Lorenzo.ru.g-guest/mplayer/debian/output'
gbp:info: Creating /builds/Lorenzo.ru.g-guest/mplayer/debian/output/mplayer_1.5+svn38408.orig.tar.xz
gbp:error: Error creating mplayer_1.5+svn38408.orig.tar.xz: Pristine-tar couldn't checkout "mplayer_1.5+svn38408.orig.tar.xz": fatal: path 'mplayer_1.5+svn38408.orig.tar.xz.delta' does not exist in 'refs/heads/pristine-tar'
pristine-tar: git show refs/heads/pristine-tar:mplayer_1.5+svn38408.orig.tar.xz.delta failed
pristine-tar: successfully generated ../mplayer_1.5+svn38408.orig.tar.gz
gbp:info: Disabling 'cleaner' hook
gbp:info: Extracting 'mplayer_1.5+svn38408.orig.tar.xz' to '/builds/Lorenzo.ru.g-guest/mplayer/debian/output/mplayer-tmp'
tar: /builds/Lorenzo.ru.g-guest/mplayer/debian/output/mplayer_1.5+svn38408.orig.tar.xz: Cannot open: No such file or directory
tar: Error is not recoverable: exiting now
gbp:error: Couldn't unpack
'/builds/Lorenzo.ru.g-guest/mplayer/debian/output/mplayer_1.5+svn38408.orig.tar.xz':
it exited with 2

Is there a way to tell gbp import-orig to use xz compression?

Lorenzo