deps: update dependency io.grpc:grpc-stub to v1.50.2 (#465)

[![Mend Renovate](https://app.renovatebot.com/images/banner.svg)](https://renovatebot.com)

This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [io.grpc:grpc-stub](https://togithub.com/grpc/grpc-java) | `1.50.0` -> `1.50.2` | [![age](https://badges.renovateapi.com/packages/maven/io.grpc:grpc-stub/1.50.2/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/io.grpc:grpc-stub/1.50.2/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/io.grpc:grpc-stub/1.50.2/compatibility-slim/1.50.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/io.grpc:grpc-stub/1.50.2/confidence-slim/1.50.0)](https://docs.renovatebot.com/merge-confidence/) |

---

### Release Notes

<details>
<summary>grpc/grpc-java</summary>

### [`v1.50.2`](https://togithub.com/grpc/grpc-java/releases/tag/v1.50.2)

##### Bug fixes

gcp-observability: Supports period(.) in the service name part of regular expression for a fully-qualified method to accept "package.service"

### [`v1.50.1`](https://togithub.com/grpc/grpc-java/releases/tag/v1.50.1)

gcp-observability: support new configuration defined in grpc-gcp-observability public preview user guide

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, click this checkbox.

---

This PR has been generated by [Mend Renovate](https://www.mend.io/free-developer-tools/renovate/). View repository job log [here](https://app.renovatebot.com/dashboard#github/googleapis/java-common-protos).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzMi4yMzguNCIsInVwZGF0ZWRJblZlciI6IjMyLjI0MS4xMSJ9-->

java-common-protos/grpc-google-common-protos/build.gradle

@@ -18,7 +18,7 @@ repositories {
 }
 
 dependencies {
-  compile 'io.grpc:grpc-stub:1.50.0'
+  compile 'io.grpc:grpc-stub:1.50.2'
   compile 'io.grpc:grpc-protobuf:1.50.0'
   compile project(':proto-google-common-protos')
 }