fix minor typos in comments (#1832)

Author: davidhewitt

src/serializers/extra.rs

@@ -406,7 +406,7 @@ impl CollectWarnings {
             Ok(())
         } else if extra.check.enabled() {
             // note: I think this should never actually happen since we use `to_python(..., mode='json')` during
-            // JSON serialisation to "try" union branches, but it's here for completeness/correctness
+            // JSON serialization to "try" union branches, but it's here for completeness/correctness
             // in particular, in future we could allow errors instead of warnings on fallback
             Err(S::Error::custom(UNEXPECTED_TYPE_SER_MARKER))
         } else {

src/serializers/type_serializers/model.rs

@@ -205,7 +205,7 @@ impl TypeSerializer for ModelSerializer {
         } else if self.allow_value(value, &model_extra)? {
             let inner_value = self.get_inner_value(value, &model_extra)?;
             // There is strong coupling between a model serializer and its child, we should
-            // not fall back to type inference in the midddle.
+            // not fall back to type inference in the middle.
             self.serializer
                 .to_python_no_infer(&inner_value, include, exclude, &model_extra)
         } else {