Bump kotlin from 2.1.20 to 2.1.21 (#230)

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

@@ -4,7 +4,7 @@ exposed = "0.61.0"
 firebase-admin = "9.4.3"
 h2 = "2.3.232"
 imageio-webp = "0.1.6"
-kotlin = "2.1.20"
+kotlin = "2.1.21"
 kotlinx-kover = "0.9.1"
 kotlin-serialization = "1.8.1"
 ktor = "3.1.3"