fix: Change quoting in array shape PHPDoc

Why? PHPStorm was unable to correctly parse the meaning of 'null?'.
With single quotes, he thought the "?" stands for the optional array key
instead of string key "null?".

Author: martinsifra

src/Column/Snowflake/SnowflakeColumn.php

@@ -54,7 +54,7 @@ public function getColumnDefinition(): DefinitionInterface
      *     name: string,
      *     type: string,
      *     default: string,
-     *     'null?': string
+     *     "null?": string,
      * } $dbResponse
      */
     public static function createFromDB(array $dbResponse): SnowflakeColumn

src/Table/Snowflake/SnowflakeTableReflection.php

@@ -118,13 +118,16 @@ public function getColumnsNames(): array
     public function getColumnsDefinitions(): ColumnCollection
     {
         $this->cacheTableProps();
-        /** @var array<array{
+
+        /**
+         * @var array<array{
          *     name: string,
          *     kind: string,
          *     type: string,
          *     default: string,
-         *     'null?': string
-         * }> $columnsMeta */
+         *     "null?": string,
+         * }> $columnsMeta
+         */
         $columnsMeta = $this->connection->fetchAllAssociative(
             sprintf(
                 'DESC TABLE %s',