Add the 3v4l reproducer of a non-redundant zero assignment to the test

https://3v4l.org/GiSbY: `$f === 0.0` holds for -0.0, yet `$f = 0.0` in
that branch changes what `echo $f` prints from "-0" to "0".

Author: zonuexe

tests/PHPStan/Rules/DeadCode/data/unused-variable-redundant-signed-zero.php

@@ -83,3 +83,14 @@ function repeatedPositiveZeroIsNotReportedEither(): void
 	$x = 0.0;
 	sink($x);
 }
+
+// https://3v4l.org/GiSbY
+function h(): void {
+	$f = -0.0;
+	var_dump($f === 0.0); // bool(true)
+	echo $f, "\n";        // -0
+	if ($f === 0.0) {
+		$f = 0.0;         // not redundant: turns -0.0 into 0.0
+	}
+	echo $f, "\n";        // 0
+}