Update grpc-netty-shaded, grpc-protobuf, ... to 1.68.2 (#3740)

## About this PR
📦 Updates 
* [io.grpc:grpc-netty-shaded](https://github.com/grpc/grpc-java)
* [io.grpc:grpc-protobuf](https://github.com/grpc/grpc-java)
* [io.grpc:grpc-stub](https://github.com/grpc/grpc-java)

 from `1.68.1` to `1.68.2`

📜 [GitHub Release
Notes](https://github.com/grpc/grpc-java/releases/tag/v1.68.2) -
[Version
Diff](grpc/grpc-java@v1.68.1...v1.68.2)

## 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/7ec418cd5441d449f037bca6d34326534c07a5dd/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 = "io.grpc" } ]
```
Or, add this to slow down future updates of this dependency:
```
dependencyOverrides = [{
  pullRequests = { frequency = "30 days" },
  dependency = { groupId = "io.grpc" }
}]
```
</details>

<sup>
labels: library-update
</sup>

build.sbt

@@ -21,7 +21,7 @@ val JS_JAVA_TIME_VERSION            = "1.0.0"
 val SCALAJS_DOM_VERSION             = "2.8.0"
 val FINAGLE_VERSION                 = "24.2.0"
 val FLUENCY_VERSION                 = "2.7.3"
-val GRPC_VERSION                    = "1.68.1"
+val GRPC_VERSION                    = "1.68.2"
 val JMH_VERSION                     = "1.37"
 val JAVAX_ANNOTATION_API_VERSION    = "1.3.2"
 val PARQUET_VERSION                 = "1.14.4"