Require latest v2 version of Xdebug

This is a temporary restriction since we're transitioning soon
to Xdebug 3, but some changes will be needed prior to that.

Author: agustingomes

src/php/utils/docker/docker-php-dev-mode

@@ -29,7 +29,7 @@ case "$1" in
 			exit 1
 		fi
 
-		pecl install xdebug-stable
+		pecl install xdebug-2.9.8
 		docker-php-ext-enable xdebug
 		apk del $apkDel