test: split test cases for getenv

Author: msbit

tests/PHPStan/Analyser/nsrt/bug-4538.php renamed to tests/PHPStan/Analyser/nsrt/bug-4538-php7.php

@@ -1,4 +1,4 @@
-<?php
+<?php // lint < 8.0
 
 namespace Bug4538;
 

tests/PHPStan/Analyser/nsrt/bug-4538-php8.php

@@ -0,0 +1,18 @@
+<?php // lint >= 8.0
+
+namespace Bug4538;
+
+use function PHPStan\Testing\assertType;
+
+class Foo
+{
+	/**
+	 * @param string $index
+	 */
+	public function bar(string $index): void
+	{
+		assertType('string|array<string,string>|false', getenv($index));
+		assertType('array<string, string>', getenv());
+		assertType('array<string, string>', getenv(null));
+	}
+}