Update dependency io.reactivex.rxjava3:rxjava to v3.1.6 (#400)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [io.reactivex.rxjava3:rxjava](https://togithub.com/ReactiveX/RxJava) |
dependencies | patch | `3.1.5` -> `3.1.6` |

---

### Release Notes

<details>
<summary>ReactiveX/RxJava</summary>

###
[`v3.1.6`](https://togithub.com/ReactiveX/RxJava/releases/tag/v3.1.6)


[Maven](http://search.maven.org/#artifactdetails%7Cio.reactivex.rxjava3%7Crxjava%7C3.1.6%7C)
[JavaDocs](http://reactivex.io/RxJava/3.x/javadoc/3.1.6)

##### API changes

- Add an overload to `throttleLatest` operator with an `onDropped`
callback. (<a
href='https://github.com/ReactiveX/RxJava/issues/7457'>[#&#8203;7457](https://togithub.com/ReactiveX/RxJava/issues/7457)</a>)
- Add an overload to `throttleFirst` operator with an `onDropped`
callback. (<a
href='https://github.com/ReactiveX/RxJava/issues/7482'>[#&#8203;7482](https://togithub.com/ReactiveX/RxJava/issues/7482)</a>)
- Add an overload to `throttleLast` operator with an `onDropped`
callback. (<a
href='https://github.com/ReactiveX/RxJava/issues/7488'>[#&#8203;7488](https://togithub.com/ReactiveX/RxJava/issues/7488)</a>)
- Add an overload to `throttleWithTimeout` operator with an `onDropped`
callback. (<a
href='https://github.com/ReactiveX/RxJava/issues/7510'>[#&#8203;7510](https://togithub.com/ReactiveX/RxJava/issues/7510)</a>)

##### Bugfixes

- Fix a race condition in `Single.timeout` that prevented the timeout
signal from happening. (<a
href='https://github.com/ReactiveX/RxJava/issues/7515'>[#&#8203;7515](https://togithub.com/ReactiveX/RxJava/issues/7515)</a>)

##### Documentation

- Fix formatting in `TestObserver/Consumer/Subscriber` javadoc html. (<a
href='https://github.com/ReactiveX/RxJava/issues/7442'>[#&#8203;7442](https://togithub.com/ReactiveX/RxJava/issues/7442)</a>)
- Fix typo in `BehaviorSubject.java`. (<a
href='https://github.com/ReactiveX/RxJava/issues/7452'>[#&#8203;7452](https://togithub.com/ReactiveX/RxJava/issues/7452)</a>)
- Fix grammar about cancellation in `Schedulers` javadoc. (<a
href='https://github.com/ReactiveX/RxJava/issues/7453'>[#&#8203;7453](https://togithub.com/ReactiveX/RxJava/issues/7453)</a>)
- Change `@coded` tag to `@code` tag. (<a
href='https://github.com/ReactiveX/RxJava/issues/7463'>[#&#8203;7463](https://togithub.com/ReactiveX/RxJava/issues/7463)</a>)
- Fix `fromCompletionStage` javadoc. (<a
href='https://github.com/ReactiveX/RxJava/issues/7508'>[#&#8203;7508](https://togithub.com/ReactiveX/RxJava/issues/7508)</a>)

##### Other

- Add missing `@NonNull` annotation to `Maybe` type argument. (<a
href='https://github.com/ReactiveX/RxJava/issues/7436'>[#&#8203;7436](https://togithub.com/ReactiveX/RxJava/issues/7436)</a>)
- Remove redundant interface declarations. (<a
href='https://github.com/ReactiveX/RxJava/issues/7438'>[#&#8203;7438](https://togithub.com/ReactiveX/RxJava/issues/7438)</a>)
- Standardize `MissingBackpressureException` message, introduce
`QueueOverflowException`. (<a
href='https://github.com/ReactiveX/RxJava/issues/7459'>[#&#8203;7459](https://togithub.com/ReactiveX/RxJava/issues/7459)</a>)
- Update `Flowable.throttleLatest` `MissingBackpressureException`
message. (<a
href='https://github.com/ReactiveX/RxJava/issues/7460'>[#&#8203;7460](https://togithub.com/ReactiveX/RxJava/issues/7460)</a>)
- Fix cancellation order in `throttleFirst`. (<a
href='https://github.com/ReactiveX/RxJava/issues/7484'>[#&#8203;7484](https://togithub.com/ReactiveX/RxJava/issues/7484)</a>)

</details>

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gradle/libs.versions.toml

@@ -177,7 +177,7 @@ retrofit = { module = "com.squareup.retrofit2:retrofit", version.ref = "retrofit
 retrofit-converters-moshi = { module = "com.squareup.retrofit2:converter-moshi", version.ref = "retrofit" }
 retrofit-converters-scalars = { module = "com.squareup.retrofit2:converter-scalars", version.ref = "retrofit" }
 robolectric = { module = "org.robolectric:robolectric", version.ref="robolectric" }
-rxjava = "io.reactivex.rxjava3:rxjava:3.1.5"
+rxjava = "io.reactivex.rxjava3:rxjava:3.1.6"
 testing-espresso-core = "androidx.test.espresso:espresso-core:3.5.1"
 # Robolectric/Espresso ship with an old and totally borked version of hamcrest dependency, force a newer one
 testing-hamcrest = "org.hamcrest:hamcrest:2.2"