Description:
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After upgrading from v7.3.3 to v7.3.7 it appears nested "php tags" inside a string are no longer being stripped correctly by strip_tags().

This is still working in v7.3.3, v7.2 & v7.1. I've added a simple test below.

Test script:
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<?php
$str = '<?= \'<?= 1 ?>\' ?>2';
var_dump(strip_tags($str));

Expected result:
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string(1) "2"

Actual result:
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string(5) "' ?>2"