Update mockito monorepo to v5.21.0

Author: renovate[bot]

dependencyManagement/build.gradle.kts

@@ -10,7 +10,7 @@ val otelContribAlphaVersion = "1.52.0-alpha"
 
 val autoValueVersion = "1.11.1"
 val dockerJavaVersion = "3.7.0"
-val mockitoVersion = "5.20.0"
+val mockitoVersion = "5.21.0"
 val protobufVersion = "4.33.2"
 val slf4jVersion = "2.0.17"