chore(userspace/engine): fix build warning.

Signed-off-by: Federico Di Pierro <[email protected]>

userspace/engine/rule_loader.h

@@ -250,7 +250,7 @@ class result : public falco::load_result {
 	                 const context& ctx);
 
 	void set_schema_validation_status(const std::vector<std::string>& status);
-	std::string schema_validation();
+	std::string schema_validation() override;
 
 protected:
 	const std::string& as_summary_string();