fix: pass null to ReflectionProperty::setValue() for static Assert::$count

[gherrink]

Forward-port of #244 to 5.x. That PR targets 4.x only, and its author offered to port it here — this is that port. Happy to close either if you would rather take one.

The problem

Execution::resetAssertions() passes Assert::class as the first argument to ReflectionProperty::setValue(). Assert::$count is static, and PHP 8.3 deprecates any first argument that is not null or an object:

Calling ReflectionProperty::setValue() with a 1st argument which is not null or an object is deprecated

It fires whenever an assertion retries, so it attaches to an arbitrary test — usually a slow one — and labels it DEPRECATED while the run still exits 0. On PHP 9 the call stops working altogether.

Why null and not the single-argument form

setValue($value) looks like the tidier fix, but it is deprecated too on 8.4. Measured on PHP 8.4.23:

call	result
setValue(Assert::class, $n)	Calling ReflectionProperty::setValue() with a 1st argument which is not null or an object is deprecated
setValue(null, $n)	clean
setValue($n)	Calling ReflectionProperty::setValue() with a single argument is deprecated

So null as the first argument is the only spelling that raises nothing.

Why the ignore comment goes too

phpstan.neon sets reportUnmatchedIgnoredErrors: true, so leaving // @phpstan-ignore-next-line on the corrected call fails the build. composer test:types is green with it removed (level max, --memory-limit=2G; the default 128M crashes a parallel worker on this machine).

Checked

• composer test:types — no errors.
• composer test:lint — rector --dry-run reports src/Support/Screenshot.php:42, which reproduces identically on unmodified 5.x. Not from this change.
• Applied to v5.0.1 in a real project's browser suite: the DEPRECATED label disappears and the run is otherwise identical — 53 passed, 106 assertions, before and after.