Inconsistent Parsing Error

### What happened?
When I have a string field in input and I pass in a wrong type, I am seeing different error code.
For example:
`{"input":{"filter":{"someString": true}}}`, I pass in a boolean for a string, and this would give me `GRAPHQL_VALIDATION_FAILED` error.

But if I do `{"input":{"filter":{"someString": 123}}}`, it would pass the validation and give me `json.Number is not a string`.

### What did you expect?
Both should give me `GRAPHQL_VALIDATION_FAILED`

### Minimal graphql.schema and models to reproduce

### versions
- `go run github.com/99designs/gqlgen version`?
v0.16.0
- `go version`?
go version go1.17.6 darwin/amd64