Revert "Don't use /tmp anymore"

This reverts commit ea5306e54f.

scripts/upgrade

@@ -189,7 +189,7 @@ do
     ynh_replace_string "__SHA256_SUM__" "$nextcloud_source_sha256" "../conf/app.src"
 
     # Create a temporary directory
-    tmpdir="${final_path}_temp_upgrade_dir"
+    tmpdir=$(mktemp -d)
 
     # Install the next nextcloud version in $tmpdir
     ynh_setup_source "$tmpdir"
@@ -208,7 +208,6 @@ do
     # Replace the old nextcloud by the new one
     ynh_secure_remove "$final_path"
     mv "$tmpdir" "$final_path"
-    ynh_secure_remove "$tmpdir"
 
     # Set write access for the following commands
     chown -R $app: "$final_path" "$datadir"