Bump mockito-core from 3.12.4 to 4.0.0 (ReactiveX#7350)

Bumps [mockito-core](https://github.com/mockito/mockito) from 3.12.4 to 4.0.0.
- [Release notes](https://github.com/mockito/mockito/releases)
- [Commits](mockito/mockito@v3.12.4...v4.0.0)

---
updated-dependencies:
- dependency-name: org.mockito:mockito-core
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

build.gradle

@@ -16,7 +16,7 @@ ext {
     reactiveStreamsVersion = "1.0.3"
     junitVersion = "4.13.2"
     testNgVersion = "7.4.0"
-    mockitoVersion = "3.12.4"
+    mockitoVersion = "4.0.0"
     jmhLibVersion = "1.21"
     guavaVersion = "31.0.1-jre"
 }