Fix spl_autoload_register PHPStan warning

> Parameter #1 $callback of function spl_autoload_register expects
> (callable(string): void)|null, Closure(string): bool given.

Two changes were needed to match the parameter type expected by
PHPStan:

1. Promote the 'get_class_loc' string to first-class callable syntax
   (see smrealms#1183).

2. Remove the boolean return value from `get_class_loc`. This was a
   "speculative" feature added in 3f6854f, but it doesn't conform to
   the expected interface nor is it needed for the autoloader to throw
   an Error if the class is not found.

src/bootstrap.php

@@ -220,7 +220,7 @@ function array_rand_value(array $arr): mixed {
 // Set up vendor and class autoloaders
 require_once(ROOT . 'vendor/autoload.php');
 require_once(LIB . 'autoload.inc.php');
-spl_autoload_register('get_class_loc');
+spl_autoload_register(get_class_loc(...));
 
 // Load common functions
 require_once(LIB . 'Default/smr.inc.php');

src/lib/autoload.inc.php

@@ -31,18 +31,17 @@ function get_game_dir(): string {
  * Includes the correct game-specific version of a class file.
  * Try to avoid calling this before `$overrideGameID` is set!
  */
-function get_class_loc(string $className): bool {
+function get_class_loc(string $className): void {
 	$className = str_replace('\\', DIRECTORY_SEPARATOR, $className);
 	// Fallback to Default directory
 	$dirs = array_unique([get_game_dir(), 'Default/']);
 	foreach ($dirs as $dir) {
 		$classFile = LIB . $dir . $className . '.php';
 		if (is_file($classFile)) {
 			require($classFile);
-			return true;
+			return;
 		}
 	}
-	return false;
 }
 
 /**