Update plugin org.openapi.generator to v7.20.0

Author: renovate[bot]

build.gradle

@@ -16,7 +16,7 @@ plugins {
   id 'com.github.ben-manes.versions' version '0.53.0'
   id 'org.sonarqube' version '6.3.1.5724'
   id "io.freefair.lombok" version "8.14"
-  id "org.openapi.generator" version "7.13.0"
+  id "org.openapi.generator" version "7.20.0"
   id "org.flywaydb.flyway" version "11.20.3"
   id 'maven-publish'
   id("com.dorongold.task-tree") version "4.0.1"