Fix test case error message mismatch in `pkg/apis/options/load_test.go`.
`TestOptions` has the `TestOptionSubStruct` field, which is the parent of
`StringSliceOptions`.
---
--- a/pkg/apis/options/load_test.go
+++ b/pkg/apis/options/load_test.go
@@ -470,7 +470,7 @@
 				configFile:     []byte(`stringSliceOption: "a"`),
 				input:          &TestOptions{},
 				expectedOutput: &TestOptions{},
-				expectedErr:    errors.New("error unmarshalling config: error unmarshaling JSON: while decoding JSON: json: cannot unmarshal string into Go struct field TestOptions.StringSliceOption of type []string"),
+				expectedErr:    errors.New("error unmarshalling config: error unmarshaling JSON: while decoding JSON: json: cannot unmarshal string into Go struct field TestOptions.TestOptionSubStruct.StringSliceOption of type []string"),
 			}),
 			Entry("with a config file containing environment variable references", loadYAMLTableInput{
 				configFile: []byte("stringOption: ${TESTUSER}"),