Refactor getOs()

Signed-off-by: Kamil Tekiela <tekiela246@gmail.com>

phpstan-baseline.neon

@@ -17355,11 +17355,6 @@ parameters:
 			count: 1
 			path: src/Server/SysInfo/SunOs.php
 
-		-
-			message: "#^Call to function in_array\\(\\) requires parameter \\#3 to be set\\.$#"
-			count: 1
-			path: src/Server/SysInfo/SysInfo.php
-
 		-
 			message: "#^Class COM referenced with incorrect case\\: com\\.$#"
 			count: 1

src/Server/SysInfo/SysInfo.php

@@ -28,9 +28,8 @@ class SysInfo
     public static function getOs(string $phpOs = PHP_OS): string
     {
         // look for common UNIX-like systems
-        $unixLike = ['FreeBSD', 'DragonFly'];
-        if (in_array($phpOs, $unixLike)) {
-            $phpOs = 'Linux';
+        if (in_array($phpOs, ['FreeBSD', 'DragonFly'], true)) {
+            return 'Linux';
         }
 
         return ucfirst($phpOs);