Fix: Allow function calls in test variable blocks (#2947) (#2990)

internal/command/testdata/test/function_call_in_variables/main.tf

@@ -0,0 +1,19 @@
+variable "input" {
+  type = string
+}
+
+variable "joined" {
+  type = string
+}
+
+output "input_output" {
+  value = var.input
+}
+
+output "joined_output" {
+  value = var.joined
+}
+
+resource "test_resource" "dummy" {
+  value = "placeholder"
+}