metadata: Exclude field::type_name from metadata validation (#595)

* metadata: Exclude `field::type_name` from metadata validation

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Adjust code-base to rust `1.62.0`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

testing/integration-tests/src/metadata/validation.rs

@@ -75,8 +75,7 @@ async fn full_metadata_check() {
     assert_eq!(
         new_api
             .validate_metadata()
-            .err()
-            .expect("Validation should fail for incompatible metadata"),
+            .expect_err("Validation should fail for incompatible metadata"),
         ::subxt::MetadataError::IncompatibleMetadata
     );
 }