fix(deps): update dependency org.openapitools:openapi-generator to v7.21.0

Author: renovate[bot]

generator/pom.xml

@@ -125,7 +125,7 @@
     </dependencies>
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <openapi-generator-version>7.20.0</openapi-generator-version>
+        <openapi-generator-version>7.21.0</openapi-generator-version>
         <maven-plugin-version>1.0.0</maven-plugin-version>
         <junit-version>4.13.2</junit-version>
     </properties>