chore: fix Rust 1.91.0 lint for derivable Default

src/configure/auto_mozilla.rs

@@ -28,8 +28,9 @@ struct MozAutoconfigure {
     pub outgoing_servers: Vec<Server>,
 }
 
-#[derive(Debug)]
+#[derive(Debug, Default)]
 enum MozConfigTag {
+    #[default]
     Undefined,
     Hostname,
     Port,
@@ -37,12 +38,6 @@ enum MozConfigTag {
     Username,
 }
 
-impl Default for MozConfigTag {
-    fn default() -> Self {
-        Self::Undefined
-    }
-}
-
 impl FromStr for MozConfigTag {
     type Err = ();