chore: Make the MariaDBDialect class extendable to be consistent with other dialect classes

Author: joc-a

exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/vendors/MariaDBDialect.kt

@@ -66,7 +66,7 @@ internal object MariaDBFunctionProvider : MysqlFunctionProvider() {
 /**
  * MariaDB dialect implementation.
  */
-class MariaDBDialect : MysqlDialect() {
+open class MariaDBDialect : MysqlDialect() {
     override val name: String = dialectName
     override val functionProvider: FunctionProvider = MariaDBFunctionProvider
     override val supportsOnlyIdentifiersInGeneratedKeys: Boolean = true