Fix Clippy lints (#2495)

diff --git a/bindgen-cli/options.rs b/bindgen-cli/options.rs
index 407817b..9ab202f 100644
--- a/bindgen-cli/options.rs
+++ b/bindgen-cli/options.rs
@@ -1019,7 +1019,7 @@
             "--with-derive-custom-union",
         ),
     ] {
-        let name = emit_diagnostics.then(|| name);
+        let name = emit_diagnostics.then_some(name);
         for custom_derive in custom_derives {
             let (regex, derives) = custom_derive
                 .rsplit_once('=')