deps: update dependency com.google.cloud:grpc-gcp to v1.6.0 (#2767)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
|
[com.google.cloud:grpc-gcp](https://togithub.com/GoogleCloudPlatform/grpc-gcp-java/tree/master/grpc-gcp)
([source](https://togithub.com/GoogleCloudPlatform/grpc-gcp-java)) |
`1.5.0` -> `1.6.0` |
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|
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|
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|
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|

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Co-authored-by: Joe Wang <106995533+JoeWang1127@users.noreply.github.com>

java-shared-dependencies/first-party-dependencies/pom.xml

@@ -22,7 +22,7 @@
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <site.installationModule>${project.artifactId}</site.installationModule>
-    <grpc-gcp.version>1.5.0</grpc-gcp.version>
+    <grpc-gcp.version>1.6.0</grpc-gcp.version>
     <google.oauth-client.version>1.36.0</google.oauth-client.version>
     <google.api-client.version>2.4.0</google.api-client.version>
   </properties>