Update zio-streams, zio-test-sbt to 2.1.6 (#1275)

## About this PR
📦 Updates 
* [dev.zio:zio-streams](https://github.com/zio/zio)
* [dev.zio:zio-test-sbt](https://github.com/zio/zio)

 from `2.1.5` to `2.1.6`

📜 [GitHub Release Notes](https://github.com/zio/zio/releases/tag/v2.1.6)
- [Version Diff](zio/zio@v2.1.5...v2.1.6)

## Usage
✅ **Please merge!**

I'll automatically update this PR to resolve conflicts as long as you
don't change it yourself.

If you'd like to skip this version, you can just close this PR. If you
have any feedback, just mention me in the comments below.

Configure Scala Steward for your repository with a
[`.scala-steward.conf`](https://github.com/scala-steward-org/scala-steward/blob/767fcfecbfd53c507152f6cf15c846176bae561d/docs/repo-specific-configuration.md)
file.

_Have a fantastic day writing Scala!_

<details>
<summary>⚙ Adjust future updates</summary>

Add this to your `.scala-steward.conf` file to ignore future updates of
this dependency:
```
updates.ignore = [ { groupId = "dev.zio" } ]
```
Or, add this to slow down future updates of this dependency:
```
dependencyOverrides = [{
  pullRequests = { frequency = "30 days" },
  dependency = { groupId = "dev.zio" }
}]
```
</details>

<sup>
labels: library-update, early-semver-patch, semver-spec-patch,
commit-count:1
</sup>

Co-authored-by: zio-scala-steward[bot] <145262613+zio-scala-steward[bot]@users.noreply.github.com>

build.sbt

@@ -25,7 +25,7 @@ lazy val _scala3   = "3.3.3"
 inThisBuild(
   List(
     name         := "ZIO Kafka",
-    zioVersion   := "2.1.5",
+    zioVersion   := "2.1.6",
     scalaVersion := _scala213,
     // zio-sbt defines these 'scala213' and 'scala3' settings, but we need to define them here to override the defaults and better control them
     scala213 := _scala213,