fixed venv upgrade call

scripts/_common.sh

@@ -751,9 +751,9 @@ flohmarkt_ynh_create_venv() {
 }
 
 flohmarkt_ynh_venv_upgrade() {
-  ynh_print_warn --message="flohmarkt_ynh_venv_upgrade: I'll sit here and do nothing without @grindholds confirmation"
+  ynh_print_warn --message="upgrading venv"
   (
-    $flohmarkt_venv_dir/bin/python3 -m venv --upgrade-deps
+    $flohmarkt_venv_dir/bin/python3 -m venv --upgrade-deps "$flohmarkt_venv_dir"
   )
 }