Update logback monorepo to v1.5.21 (#209)

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

Author: renovate[bot]

gradle/libs.versions.toml

@@ -48,7 +48,7 @@ dagger = "2.57.2"              # https://dagger.dev
 
 # --- Logging ---
 slf4j = "2.0.17"              # https://www.slf4j.org TODO remove
-logback = "1.5.20"           # https://logback.qos.ch
+logback = "1.5.21"           # https://logback.qos.ch
 
 # --- Concurrency ---
 rxjava = "3.1.12"            # https://github.com/ReactiveX/RxJava