Update slf4j monorepo to v2.0.15 (open-telemetry#6622)

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

Author: renovate[bot]

dependencyManagement/build.gradle.kts

@@ -29,7 +29,7 @@ val errorProneVersion = "2.29.2"
 val jmhVersion = "1.37"
 // Mockito 5.x.x requires Java 11 https://github.com/mockito/mockito/releases/tag/v5.0.0
 val mockitoVersion = "4.11.0"
-val slf4jVersion = "2.0.13"
+val slf4jVersion = "2.0.15"
 val opencensusVersion = "0.31.1"
 val prometheusClientVersion = "0.16.0"