deps: update dependency io.grpc:grpc-protobuf to v1.50.2 (#483)

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This PR contains the following updates:

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

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### 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>

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java-iam/grpc-google-iam-v1/build.gradle

@@ -19,7 +19,7 @@ repositories {
 
 dependencies {
   compile 'io.grpc:grpc-stub:1.50.2'
-  compile 'io.grpc:grpc-protobuf:1.50.0'
+  compile 'io.grpc:grpc-protobuf:1.50.2'
   compile project(':proto-google-iam-v1')
 }