Update kotlin monorepo to v2.1.21 (#3174)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

flink-end-to-end-tests/flink-glue-schema-registry-avro-test/pom.xml

@@ -34,7 +34,7 @@ under the License.
 	<properties>
 		<aws.sdk.version>1.12.783</aws.sdk.version>
 		<aws.sdkv2.version>2.31.46</aws.sdkv2.version>
-		<kotlin.version>2.1.20</kotlin.version>
+		<kotlin.version>2.1.21</kotlin.version>
 	</properties>
 
 	<dependencyManagement>

flink-end-to-end-tests/flink-glue-schema-registry-json-test/pom.xml

@@ -34,7 +34,7 @@ under the License.
 	<properties>
 		<aws.sdk.version>1.12.783</aws.sdk.version>
 		<aws.sdkv2.version>2.31.46</aws.sdkv2.version>
-		<kotlin.version>2.1.20</kotlin.version>
+		<kotlin.version>2.1.21</kotlin.version>
 	</properties>
 
 	<dependencyManagement>

flink-formats/flink-avro-glue-schema-registry/pom.xml

@@ -35,7 +35,7 @@ under the License.
 	<properties>
 		<glue.schema.registry.version>1.1.23</glue.schema.registry.version>
 		<aws.sdkv2.version>2.31.46</aws.sdkv2.version>
-		<kotlin.version>2.1.20</kotlin.version>
+		<kotlin.version>2.1.21</kotlin.version>
 	</properties>
 
 	<dependencyManagement>

flink-formats/flink-json-glue-schema-registry/pom.xml

@@ -35,7 +35,7 @@ under the License.
 		<glue.schema.registry.version>1.1.23</glue.schema.registry.version>
 		<aws.sdkv2.version>2.31.46</aws.sdkv2.version>
 		<netty.version>4.1.68.Final</netty.version>
-		<kotlin.version>2.1.20</kotlin.version>
+		<kotlin.version>2.1.21</kotlin.version>
 		<classgraph.version>4.8.120</classgraph.version>
 	</properties>