chore(deps): bump kotlin from 2.0.0 to 2.0.21 in /ApiDemos/kotlin

Bumps `kotlin` from 2.0.0 to 2.0.21.

Updates `org.jetbrains.kotlin:kotlin-gradle-plugin` from 2.0.0 to 2.0.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v2.0.21/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.0.0...v2.0.21)

Updates `org.jetbrains.kotlin:kotlin-stdlib-jdk7` from 2.0.0 to 2.0.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v2.0.21/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.0.0...v2.0.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-gradle-plugin
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin:kotlin-stdlib-jdk7
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

ApiDemos/kotlin/gradle/libs.versions.toml

@@ -1,6 +1,6 @@
 [versions]
 gradle = "8.5.2"
-kotlin = "2.0.0"
+kotlin = "2.0.21"
 appcompat = "1.7.0"
 cardview = "1.0.0"
 recyclerview = "1.3.2"