Quote MySQL constraint names for foreign keys

MariaDB 12.1 introduces InnoDB Foreign key names
of a digit which requires quoting.

closes #7021

Author: grooverdan

src/Schema/MySQLSchemaManager.php

@@ -280,7 +280,7 @@ protected function _getPortableTableForeignKeysList(array $rows): array
                 }
 
                 $list[$row['constraint_name']] = [
-                    'name' => $row['constraint_name'],
+                    'name' => $this->getQuotedIdentifierName($row['constraint_name']),
                     'local' => [],
                     'foreign' => [],
                     'foreignTable' => $row['referenced_table_name'],
@@ -524,4 +524,14 @@ private function getDefaultTableOptions(): DefaultTableOptions
 
         return $this->defaultTableOptions;
     }
+
+    /** Returns the quoted representation of the given identifier name. */
+    private function getQuotedIdentifierName(?string $identifier): ?string
+    {
+        if ($identifier === null) {
+            return null;
+        }
+
+        return $this->platform->quoteSingleIdentifier($identifier);
+    }
 }