ci: use mariadb 10.6 (#33220)

https://github.com/frappe/frappe/pull/19116

[skip ci]
diff --git a/.github/workflows/server-tests-mariadb.yml b/.github/workflows/server-tests-mariadb.yml
index b40faa7..bbb8a7e 100644
--- a/.github/workflows/server-tests-mariadb.yml
+++ b/.github/workflows/server-tests-mariadb.yml
@@ -45,9 +45,9 @@
 
     services:
       mysql:
-        image: mariadb:10.3
+        image: mariadb:10.6
         env:
-          MYSQL_ALLOW_EMPTY_PASSWORD: YES
+          MARIADB_ROOT_PASSWORD: 'root'
         ports:
           - 3306:3306
         options: --health-cmd="mysqladmin ping" --health-interval=5s --health-timeout=2s --health-retries=3