Standalone: fix loading from arbitrary file paths

Pre-Configurate had this same behavior: 765128ce42 (diff-262f536cb22e92d0eab2b1fd455563d317e907a88761a3d6ef16ec91dada4aeaL193)

Loading from alternate folders now works as expected.

bootstrap/standalone/src/main/java/org/geysermc/geyser/platform/standalone/GeyserStandaloneBootstrap.java

@@ -197,7 +197,7 @@ public class GeyserStandaloneBootstrap implements GeyserBootstrap {
     @Override
     public <T extends GeyserConfig> T loadConfig(Class<T> configClass) {
         return new ConfigLoader(this)
-            .configFile(new File(getConfigFolder().toFile(), configFilename))
+            .configFile(new File(configFilename))
             .transformer(this::handleArgsConfigOptions)
             .load(configClass);
     }