Lets see if this fixes the issue

stack/gitea-mariadb.yml

@@ -25,7 +25,7 @@ services:
       USER_UID: ${USER_UID}
       USER_GID: ${USER_GID}
       TZ: ${TZ}
-      GITEA__database__HOST: 'mariadb':3306
+      GITEA__database__HOST: 'mariadb'
       GITEA__database__USER: ${DATABASE_USER}
       GITEA__database__PASSWD: ${DATABASE_PASSWORD}
       GITEA__database__NAME: ${DATABASE_NAME}