fix weird rust issue where PartialEq is not being detected since 1.44.0

I did not manage to get a repro of this since all old versions of rust
fail to compile, eventhough the CI clearly confirms that it used to
compile with 1.43.0

derive/src/openapi_type.rs

@@ -84,7 +84,7 @@ fn parse_attributes(input: &[Attribute]) -> Result<Attrs> {
 }
 
 fn expand_variant(variant: &Variant) -> Result<TokenStream> {
-	if variant.fields != Fields::Unit {
+	if !matches!(variant.fields, Fields::Unit) {
 		return Err(Error::new(
 			variant.span(),
 			"#[derive(OpenapiType)] does not support enum variants with fields"