Handle a phpstan error level 9 about array

I've created a function in my repository :

/**
     * @return array<int, array<int, string>>
     */
    public function findByBuildingGroupByCompany(string $buildingId): array
    {
        return $this->createQueryBuilder('qr')
            ->select('DISTINCT(qr.company)')
            ->leftJoin('qr.building', 'b')
            ->leftJoin('qr.quotes', 'q')
            ->andWhere('b.id = :buildingId')
            ->andWhere('qr.company IS NOT NULL')
            ->setParameter('buildingId', $buildingId)
            ->getQuery()
            ->getResult()
            ;
    }

This function is called in my controller and if I dump it, I've got

array:3 [▼
  0 => array:1 [▼
    1 => "a00e9bcb-bffd-442a-aa9c-b0ca627fda36"
  ]
  1 => array:1 [▼
    1 => "777ea601-39d0-4d54-939f-64a56912a843"
  ]
  2 => array:1 [▼
    1 => "b78bf56c-b99d-40c7-b317-458c4df7e286"
  ]
]

So my function return what I typed array<int, array<int, string>>but phpstan throw this error : Method App\Repository\QuoteRequestRepository::findByBuildingGroupByCompany() should return array<int, array<int, string>> but returns mixed.
And if I return mixed, it throws those 2 errors :

Method
         App\Repository\QuoteRequestRepository::findByBuildingGroupByCompany()
         return type has no value type specified in iterable type array.
          See:
         https://phpstan.org/blog/solving-phpstan-no-value-type-specified-in-i
         terable-type
  49     Method
         App\Repository\QuoteRequestRepository::findByBuildingGroupByCompany()
         should return array but returns mixed

I really don't know how to handle it :(

Any idea ?