deps: update dependency com.google.protobuf:protobuf-bom to v3.21.4 (#…

…759)

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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)) | `3.21.3` -> `3.21.4` | [![age](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.4/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.4/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.4/compatibility-slim/3.21.3)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.4/confidence-slim/3.21.3)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

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

### [`v3.21.4`](https://togithub.com/protocolbuffers/protobuf/compare/v3.21.3...v3.21.4)

[Compare Source](https://togithub.com/protocolbuffers/protobuf/compare/v3.21.3...v3.21.4)

</details>

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first-party-dependencies/pom.xml

@@ -59,7 +59,7 @@
     <gax.version>2.18.4</gax.version>
     <grpc-gcp.version>1.2.1</grpc-gcp.version>
     <guava.version>31.1-jre</guava.version>
-    <protobuf.version>3.21.3</protobuf.version>
+    <protobuf.version>3.21.4</protobuf.version>
     <google.api-common.version>2.2.1</google.api-common.version>
     <google.common-protos.version>2.9.2</google.common-protos.version>
     <google.core.version>2.8.1</google.core.version>