Bug report

PHPStan no longer understands the types when iterating over a DatePeriod object.

function (\DatePeriod $p) {
	foreach ($p as $dt) {
		assertType('DateTimeInterface', $dt); // PHPStan currently identifies $dt as mixed
	}
};

I've bisected and identified phpstan/phpstan-src@4a143bd (phpstan/phpstan-src#4761) as the cause reverting this commit on the latest 2.1.x branch fixes the problem.

Code snippet that reproduces the problem

https://phpstan.org/r/ac78effb-a5c3-4c5c-b54c-4c7b67ee4a57

Expected output

No error should be detected.

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