Bump kotlin.version from 2.1.10 to 2.1.20

Author: dependabot[bot]

pom.xml

@@ -26,7 +26,7 @@
         <url>https://github.com/javadev/LeetCode-in-Kotlin</url>
     </scm>
     <properties>
-        <kotlin.version>2.1.10</kotlin.version>
+        <kotlin.version>2.1.20</kotlin.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     </properties>
     <ciManagement>