fix(deps): update kotlin monorepo to v2.1.21

Author: renovate[bot]

pom.xml

@@ -4,7 +4,7 @@
     <artifactId>load-flow-service</artifactId>
     <version>0.0.0</version>
     <properties>
-        <kotlin.version>2.1.20</kotlin.version>
+        <kotlin.version>2.1.21</kotlin.version>
         <ktor.version>3.0.0-beta-1</ktor.version>
         <main.class>com.github.statnett.loadflowservice.AppKt</main.class>
         <kotlin.code.style>official</kotlin.code.style>
@@ -73,7 +73,7 @@
         <dependency>
             <groupId>org.jetbrains.kotlin</groupId>
             <artifactId>kotlin-test-junit5</artifactId>
-            <version>2.1.20</version>
+            <version>2.1.21</version>
             <scope>test</scope>
         </dependency>
         <dependency>