Update testing to 3.21

Author: williamdes

testing/Dockerfile

@@ -1,6 +1,6 @@
 # Testing image for phpMyAdmin
 
-FROM alpine:3.20
+FROM alpine:3.21
 
 # Install test dependencies
 RUN set -ex; \

testing/test-docker.sh

@@ -20,7 +20,7 @@ else
     FILENAME=./testing/phpmyadmin_test.py
 fi
 
-mysql -h "${PHPMYADMIN_DB_HOSTNAME}" -P"${PHPMYADMIN_DB_PORT}" -u"${TESTSUITE_USER:=root}" -p"${TESTSUITE_PASSWORD}" -e "SELECT @@version;" > /dev/null
+mariadb -h "${PHPMYADMIN_DB_HOSTNAME}" -P"${PHPMYADMIN_DB_PORT}" -u"${TESTSUITE_USER:=root}" -p"${TESTSUITE_PASSWORD}" -e "SELECT @@version;" > /dev/null
 ret=$?
 
 if [ $ret -ne 0 ] ; then