[HTML5] Limit the returned OS cpu count to 2.

Temporarily workaround issues due to godot spawning too many threads.

platform/javascript/js/libs/library_godot_os.js

@@ -305,7 +305,9 @@ const GodotOS = {
 
 	godot_js_os_hw_concurrency_get__sig: 'i',
 	godot_js_os_hw_concurrency_get: function () {
-		return navigator.hardwareConcurrency || 1;
+		// TODO Godot core needs fixing to avoid spawning too many threads (> 24).
+		const concurrency = navigator.hardwareConcurrency || 1;
+		return concurrency < 2 ? concurrency : 2;
 	},
 
 	godot_js_os_download_buffer__sig: 'viiii',