Bump io.grpc:grpc-api from 1.55.1 to 1.56.0 in /load-generator (#1270)

Bumps [io.grpc:grpc-api](https://github.com/grpc/grpc-java) from 1.55.1 to 1.56.0.
- [Release notes](https://github.com/grpc/grpc-java/releases)
- [Commits](grpc/grpc-java@v1.55.1...v1.56.0)

---
updated-dependencies:
- dependency-name: io.grpc:grpc-api
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

load-generator/build.gradle

@@ -29,7 +29,7 @@ dependencies {
     implementation "com.google.guava:guava:32.0.1-jre"
 
     implementation "io.grpc:grpc-bom:1.56.0"
-    implementation "io.grpc:grpc-api:1.55.1"
+    implementation "io.grpc:grpc-api:1.56.0"
 
     implementation "io.grpc:grpc-netty-shaded:1.55.1"