Bump mongo-java-driver from 3.12.1 to 3.12.3 in /core (#2594)

Bumps [mongo-java-driver](https://github.com/mongodb/mongo-java-driver) from 3.12.1 to 3.12.3.
- [Release notes](https://github.com/mongodb/mongo-java-driver/releases)
- [Commits](mongodb/mongo-java-driver@r3.12.1...r3.12.3)

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Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

core/build.gradle

@@ -157,7 +157,7 @@ dependencies {
     testCompile 'org.apache.httpcomponents:httpclient:4.5.9'
     testCompile 'redis.clients:jedis:3.2.0'
     testCompile 'com.rabbitmq:amqp-client:5.8.0'
-    testCompile 'org.mongodb:mongo-java-driver:3.12.1'
+    testCompile 'org.mongodb:mongo-java-driver:3.12.3'
     testCompile ('org.mockito:mockito-core:3.3.3') {
         exclude(module: 'hamcrest-core')
     }