EOL not allowed in instructions

[wooorm]

A processing instruction consists of the string <?, a string of characters not including the string ?>, and the string ?>.
— https://spec.commonmark.org/0.29/#processing-instruction

However:

a <?
?>

The actual output is:

<p>a &lt;?
?&gt;</p>

The expected output according to the spec is:

<p>a <?
?></p>