chore(deps): update kotlin monorepo to v2.1.21 (#221)

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

Author: renovate[bot]

gradle/libs.versions.toml

@@ -1,6 +1,6 @@
 [versions]
 
-kotlin = "2.1.20"
+kotlin = "2.1.21"
 agp = "8.10.0"
 compose = "1.7.1"
 coil = "3.0.0-alpha08"