Fix copy-paste error in ServiceInjector

fixes 0965267

Author: YoshiRulz

src/BizHawk.Emulation.Common/ServiceInjector.cs

@@ -46,7 +46,7 @@ private static (List<ServicePropInfo> Req, List<ServicePropInfo> Opt) GetService
 					}
 					else if (attr is OptionalServiceAttribute)
 					{
-						if (pi.GetSetMethod(nonPublic: true) is MethodInfo setter) pair.Req.Add(new(pi.PropertyType, setter));
+						if (pi.GetSetMethod(nonPublic: true) is MethodInfo setter) pair.Opt.Add(new(pi.PropertyType, setter));
 						else Util.DebugWriteLine(ERR_FMT_STR_GETONLY_PROP, "OptionalService", @class.Name, pi.Name);
 						break;
 					}