Bump com.graphql-java:graphql-java-extended-validation from 20.0 to 21.0

Bumps [com.graphql-java:graphql-java-extended-validation](https://github.com/graphql-java/graphql-java-extended-validation) from 20.0 to 21.0.
- [Release notes](https://github.com/graphql-java/graphql-java-extended-validation/releases)
- [Commits](graphql-java/graphql-java-extended-validation@20.0...v21.0)

---
updated-dependencies:
- dependency-name: com.graphql-java:graphql-java-extended-validation
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

backend/build.gradle.kts

@@ -42,7 +42,7 @@ dependencies {
     }
     implementation("io.micronaut.graphql:micronaut-graphql")
     implementation("com.graphql-java-kickstart:graphql-java-tools:13.0.3")
-    implementation("com.graphql-java:graphql-java-extended-validation:20.0")
+    implementation("com.graphql-java:graphql-java-extended-validation:21.0")
     implementation("io.micronaut.validation:micronaut-validation")
     runtimeOnly("org.postgresql:postgresql")
     runtimeOnly("io.micronaut.sql:micronaut-jdbc-hikari")