Description:
------------
PDO originally returns integers and floats as a string. As of PHP 8.1 it will return them as integers.

Note: A ZEROFILL integer is where an integer will be left padded with 0's until it reaches a certain length.

Since PHP doesn't support leading zero's in an integer they're removed.

8.0.2
string(10) "0742130050"

8.1.0-dev
int(742130050)

PDO should not lose data.

The solution I suggest is 

Test script:
---------------
CREATE TABLE test ( `postcode` INT(4) UNSIGNED ZEROFILL NULL );
INSERT INTO test (`postcode`) VALUES ('0800');
SELECT * FROM test;
MariaDB [schools]> SELECT * FROM test;
+----------+
| postcode |
+----------+
|     0800 |
+----------+
1 row in set (0.000 sec)

$stmt = $pdo->prepare('SELECT * FROM test;');
$stmt->execute();
$result = $stmt->fetchObject();
var_dump($result->postcode);

Expected result:
----------------
string(4) "0800"

Actual result:
--------------
int(800)