Fix ExpandEnvironmentVariables test case

Author: egregius313

csharp/ql/test/library-tests/dataflow/flowsources/local/environment/EnvironmentVariables.expected

@@ -4,6 +4,7 @@
 | EnvironmentVariables.cs:18:48:18:84 | call to method GetEnvironmentVariables |
 | EnvironmentVariables.cs:19:60:19:129 | call to method GetEnvironmentVariables |
 | EnvironmentVariables.cs:20:59:20:128 | call to method GetEnvironmentVariables |
+| EnvironmentVariables.cs:25:31:25:78 | call to method ExpandEnvironmentVariables |
 | EnvironmentVariables.cs:30:26:30:51 | [post] object creation of type ConfigurationBuilder |
 | EnvironmentVariables.cs:30:26:31:42 | call to method AddEnvironmentVariables |
 | EnvironmentVariables.cs:41:13:41:19 | [post] access to local variable builder |