Add test file for bad sensitive value

Adds a test file for an incorrectly typed
(non-boolean) sensitive value to ensure it errors

configs/testdata/invalid-files/variable-bad-sensitive.tf

@@ -0,0 +1,7 @@
+terraform {
+  experiments = [sensitive_variables]
+}
+
+variable "sensitive-value" {
+  sensitive = "123" # must be boolean
+}