Update dependency com.google.code.gson:gson to v2.8.9 (#626)

Co-authored-by: mend-for-github.aaakk.us.kg[bot] <50673670+mend-for-github.aaakk.us.kg[bot]@users.noreply.github.com>
(cherry picked from commit 5e7d805)

notifications/notifications/build.gradle

@@ -128,7 +128,7 @@ dependencies {
     testImplementation "org.jetbrains.kotlin:kotlin-reflect:${kotlin_version}" // required by mockk
     testImplementation "net.bytebuddy:byte-buddy-agent:1.12.7"
     testImplementation "org.mockito:mockito-core:5.1.0"
-    testImplementation 'com.google.code.gson:gson:2.8.7'
+    testImplementation 'com.google.code.gson:gson:2.8.9'
     testImplementation 'org.springframework.integration:spring-integration-mail:5.5.0'
     testImplementation 'org.springframework.integration:spring-integration-test-support:5.5.0'
     compileOnly project(path: ":${rootProject.name}-core-spi", configuration: 'shadow')