Fix migration bug with prefix assembly

[cdhanna]

The UsamMigrator.GetAssemblyDefinitionAssets() has an issue finding assemblies; if there are multiple with prefix

		var guid = AssetDatabase.FindAssets($"t:AssemblyDefinitionAsset {name}");

					if (guid.Length == 0)
					{
						continue; //there is no asset of this assembly to reference
					}

					if (guid.Length > 1)
					{
						throw new Exception($"Found more than one assembly definition with the name: {name}");
					}