fix more causes of clippy warnings

[striezel]

Clippy linting had more errors:

error: iterating on a map's values
Error:   --> crates/macros/src/module.rs:56:36
   |
56 |       let registered_classes_impls = state
   |  ____________________________________^
57 | |         .classes
58 | |         .iter()
59 | |         .map(|(_, class)| generate_registered_class_impl(class))
   | |________________________________________________________________^
   |
   = note: `-D clippy::iter-kv-map` implied by `-D warnings`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#iter_kv_map
help: try
   |
56 ~     let registered_classes_impls = state
57 +         .classes.values().map(|class| generate_registered_class_impl(class))
   |

error: iterating on a map's values
Error:    --> crates/macros/src/module.rs:366:23
    |
366 |         let classes = self.classes.iter().map(|(_, class)| class.describe());
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `self.classes.values().map(|class| class.describe())`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#iter_kv_map

error: could not compile `ext-php-rs-derive` due to 2 previous errors

[TobiasBengtsson]

Thanks! 👍