deps: update actions/github-script action to v6 (#1010)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/github-script](https://togithub.com/actions/github-script) | action | major | `v5` -> `v6` |

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### Release Notes

<details>
<summary>actions/github-script</summary>

### [`v6`](https://togithub.com/actions/github-script/compare/v5...v6)

[Compare Source](https://togithub.com/actions/github-script/compare/v5...v6)

</details>

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README.md

@@ -58,13 +58,13 @@ implementation 'com.google.cloud:google-cloud-pubsub'
 If you are using Gradle without BOM, add this to your dependencies
 
 ```Groovy
-implementation 'com.google.cloud:google-cloud-pubsub:1.115.3'
+implementation 'com.google.cloud:google-cloud-pubsub:1.115.4'
 ```
 
 If you are using SBT, add this to your dependencies
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-pubsub" % "1.115.3"
+libraryDependencies += "com.google.cloud" % "google-cloud-pubsub" % "1.115.4"
 ```
 
 ## Authentication