Bump kotlin from 2.1.20 to 2.1.21 (#1037)

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

gradle/libs.versions.toml

@@ -23,7 +23,7 @@ dokka = "2.0.0"
 guava = "33.3.1-android"
 json = "20250517"
 junit = "4.13.2"
-kotlin = "2.1.20"
+kotlin = "2.1.21"
 kotlinx-coroutines = "1.10.2"
 kotlinx-datetime = "0.6.2"
 kotlinx-kover = "0.9.1"