Fix AssertionError in PillarboxMediaMetaDataTrackerTest

[MGaetan89]

As a Pillarbox developer, I want to be able to run the project's tests with confidence.

Context

From time to time, the PillarboxMediaMetaDataTrackerTest > chapter transition after seek back fails because we don't receive the expected values.
Here's the stacktrace:

PillarboxMediaMetaDataTrackerTest > chapter transition after seek back FAILED
    java.lang.AssertionError: expected:<[Chapter(id=Chapter3, start=2000, end=5000, mediaMetadata=androidx.media3.common.MediaMetadata@743fcd71), null, Chapter(id=Chapter3, start=2000, end=5000, mediaMetadata=androidx.media3.common.MediaMetadata@743fcd71), null, Chapter(id=Chapter4, start=10000, end=15000, mediaMetadata=androidx.media3.common.MediaMetadata@743fcd71), null]> but was:<[Chapter(id=Chapter3, start=2000, end=5000, mediaMetadata=androidx.media3.common.MediaMetadata@743fcd71), null, Chapter(id=Chapter3, start=2000, end=5000, mediaMetadata=androidx.media3.common.MediaMetadata@743fcd71), Chapter(id=Chapter4, start=10000, end=15000, mediaMetadata=androidx.media3.common.MediaMetadata@743fcd71), null]>
        at org.junit.Assert.fail(Assert.java:89)
        at org.junit.Assert.failNotEquals(Assert.java:835)
        at org.junit.Assert.assertEquals(Assert.java:120)
        at kotlin.test.junit.JUnitAsserter.assertEquals(JUnitSupport.kt:32)
        at kotlin.test.AssertionsKt__AssertionsKt.assertEquals(Assertions.kt:63)
        at kotlin.test.AssertionsKt.assertEquals(Unknown Source)
        at kotlin.test.AssertionsKt__AssertionsKt.assertEquals$default(Assertions.kt:62)
        at kotlin.test.AssertionsKt.assertEquals$default(Unknown Source)
        at ch.srgssr.pillarbox.player.tracker.PillarboxMediaMetaDataTrackerTest.chapter transition after seek back(PillarboxMediaMetaDataTrackerTest.kt:96)

Acceptance criteria

• PillarboxMediaMetaDataTrackerTest > chapter transition after seek back behave consistently across multiple executions.