Validation of complex enum values causes panic

[fenollp]

enum:
- {}
- []
- 42

The first two enum values are not Go-comparable, so this comparison

kin-openapi/openapi3/schema.go

Lines 871 to 876 in ac18113

	if enum := schema.Enum; len(enum) != 0 {
	for _, v := range enum {
	if value == v {
	return
	}
	}

crashes.