deps: update dependency com.google.protobuf:protobuf-bom to v3.21.9 (#998)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.protobuf:protobuf-bom](https://developers.google.com/protocol-buffers/) ([source](https://togithub.com/protocolbuffers/protobuf)) | `3.21.8` -> `3.21.9` | [![age](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.9/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.9/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.9/compatibility-slim/3.21.8)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.9/confidence-slim/3.21.8)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

<details>
<summary>protocolbuffers/protobuf</summary>

### [`v3.21.9`](https://togithub.com/protocolbuffers/protobuf/compare/v3.21.8...v3.21.9)

[Compare Source](https://togithub.com/protocolbuffers/protobuf/compare/v3.21.8...v3.21.9)

</details>

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Author: renovate-bot

pom.xml

@@ -159,7 +159,7 @@
     <google.api.version>2.0.0</google.api.version>
     <google.http.version>1.42.3</google.http.version>
     <grpc.version>1.50.2</grpc.version>
-    <protobuf.version>3.21.8</protobuf.version>
+    <protobuf.version>3.21.9</protobuf.version>
     <opencensus.version>0.31.1</opencensus.version>
     <annotations-api.version>1.3.2</annotations-api.version>
     <guava.version>31.1-jre</guava.version>