MINOR: Upgrade mockito test dependencies (#12460)

## Changes
- **mockito: 4.4.0 -> 4.6.1** (https://github.com/mockito/mockito/releases)
Most important updates:
  - Fixes mockito/mockito#2648 : Add support for customising strictness via @mock annotation and MockSettings mockito/mockito#2650

## Why is this change needed?

According to the [Mockito documentation](https://javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/Mockito.html#when(T)) :
> Although it is possible to verify a stubbed invocation, usually it's just redundant. Let's say you've stubbed foo.bar(). If your code cares what foo.bar() returns then something else breaks(often before even verify() gets executed). If your code doesn't care what get(0) returns then it should not be stubbed. 

While working on the [Replace EasyMock and PowerMock with Mockito for StreamsMetricsImplTest ](https://issues.apache.org/jira/browse/KAFKA-12947) I noticed that described behavior wasn't applied when you create a new `mock` like this.

```java
        final Metrics metrics = mock(Metrics.class);
        when(metrics.metric(metricName)).thenReturn(null);

        ... invoke SUT

        verify(metrics).metric(metricName); // this should be redundant (according to docs)

```

After further investigation I figured out that described behaviour wasn't implemented until`v4.6.1`.

With this change we are now able to mock objects like this:

```java
   Foo explicitStrictMock = mock(Foo.class, withSettings().strictness(Strictness.STRICT_STUBS));
```
- link to docs: [MockSettings.html#strictness](https://javadoc.io/static/org.mockito/mockito-core/4.6.1/org/mockito/quality/Strictness.html#STRICT_STUBS)

It looks like I can accomplish the same thing by using the `@RunWith(MockitoJUnitRunner.StrictStubs.class)
` instead of the `@RunWith(MockitoJUnitRunner.class)` so mockito dependency version update is not mandatory, but it would be nice to stay up-to-date and use the latest version (it's up to MR reviewer to decide if we are going to merge this now, or just close the MR and update mockito version later).

Reviewers: Ismael Juma <ismael@juma.me.uk>

gradle/dependencies.gradle

@@ -104,7 +104,7 @@ versions += [
   lz4: "1.8.0",
   mavenArtifact: "3.8.4",
   metrics: "2.2.0",
-  mockito: "4.4.0",
+  mockito: "4.6.1",
   netty: "4.1.78.Final",
   powermock: "2.0.9",
   reflections: "0.9.12",