Bump assertj-core from 3.17.2 to 3.18.1 in /modules/pulsar

Bumps [assertj-core](https://github.com/assertj/assertj-core) from 3.17.2 to 3.18.1.
- [Release notes](https://github.com/assertj/assertj-core/releases)
- [Commits](assertj/assertj@assertj-core-3.17.2...assertj-core-3.18.1)

Signed-off-by: dependabot[bot] <support@github.com>

modules/pulsar/build.gradle

@@ -4,6 +4,6 @@ dependencies {
     compile project(':testcontainers')
 
     testCompile group: 'org.apache.pulsar', name: 'pulsar-client', version: '2.6.1'
-    testCompile group: 'org.assertj', name: 'assertj-core', version: '3.17.2'
+    testCompile group: 'org.assertj', name: 'assertj-core', version: '3.18.1'
     testCompile group: 'org.apache.pulsar', name: 'pulsar-client-admin', version: '2.6.1'
 }