Fixed it Yay !
Just had to remove a .git/index.lock in /var/www/html/admin :
cd /var/www/html/admin
sudo rm -f .git/index.lock
pihole up to date :
Pi-hole Version vDev (release/v5.0, v4.3.5-455-gfff7adfb) Web Interface Version vDev (release/v5.0, v4.3.2-457-g0a81dadf) FTL Version vDev (release/v5.0, vDev-81c4eac) ```