Bump project.kotlin_version from 1.9.24 to 2.0.20 in /idea-plugin

Bumps `project.kotlin_version` from 1.9.24 to 2.0.20.

Updates `org.jetbrains.kotlin:kotlin-gradle-plugin` from 1.9.24 to 2.0.20
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v2.0.20/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.9.24...v2.0.20)

Updates `org.jetbrains.kotlin:kotlin-stdlib-jdk8` from 1.9.24 to 2.0.20
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v2.0.20/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.9.24...v2.0.20)

Updates `org.jetbrains.kotlin:kotlin-reflect` from 1.9.24 to 2.0.20
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v2.0.20/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.9.24...v2.0.20)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-gradle-plugin
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: org.jetbrains.kotlin:kotlin-stdlib-jdk8
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: org.jetbrains.kotlin:kotlin-reflect
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

idea-plugin/build.gradle

@@ -15,7 +15,7 @@ static boolean shouldIncludeJava(String idea_version_string) {
 
 buildscript {
     project.ext {
-        kotlin_version = "1.9.24"
+        kotlin_version = "2.0.20"
     }
     repositories {
         mavenCentral()