configs: New test cases for invalid interpolations in block labels

The parent commit fixes an issue where this would previously have led to
a crash. These new test cases verify that parsing is now able to complete
without crashing, though the result is still invalid.

configs/test-fixtures/invalid-files/interp-in-data-label.tf

@@ -0,0 +1,2 @@
+data "null_resource" "foo_${interpolations_invalid_here}" {
+}

configs/test-fixtures/invalid-files/interp-in-rsrc-label.tf

@@ -0,0 +1,2 @@
+resource "null_resource" "foo_${interpolations_invalid_here}" {
+}