fix: don't write the schema on dry runs.

tasks/ast_codegen/src/main.rs

@@ -248,7 +248,7 @@ fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
         cargo_fmt(".")?;
     }
 
-    if let Some(schema_path) = cli_options.schema {
+    if let CliOptions { schema: Some(schema_path), dry_run: false, .. } = cli_options {
         let path = schema_path.to_str().expect("invalid path for schema output.");
         let schema = serde_json::to_string_pretty(&schema).map_err(|e| e.to_string())?;
         write_all_to(schema.as_bytes(), path)?;