fix(deps): update kotlin monorepo to v2.1.21 (#266)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

gradle/libs.versions.toml

@@ -1,7 +1,7 @@
 [versions]
 ktlint = "1.4.1"
 ktor = "3.1.3"
-kotlin = "2.1.20"
+kotlin = "2.1.21"
 java = "19"
 multiplatform-locale = "0.9.0"