deps: update dependency com.google.protobuf:protobuf-bom to v3.21.5 (#402)

[![Mend Renovate](https://app.renovatebot.com/images/banner.svg)](https://renovatebot.com)

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)) | `3.21.4` -> `3.21.5` | [![age](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.5/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.5/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.5/compatibility-slim/3.21.4)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.5/confidence-slim/3.21.4)](https://docs.renovatebot.com/merge-confidence/) |

---

### Release Notes

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

### [`v3.21.5`](https://togithub.com/protocolbuffers/protobuf/compare/v3.21.4...v3.21.5)

[Compare Source](https://togithub.com/protocolbuffers/protobuf/compare/v3.21.4...v3.21.5)

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, click this checkbox.

---

This PR has been generated by [Mend Renovate](https://www.mend.io/free-developer-tools/renovate/). View repository job log [here](https://app.renovatebot.com/dashboard#github/googleapis/java-common-protos).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzMi4xNTMuMCIsInVwZGF0ZWRJblZlciI6IjMyLjE1NC40In0=-->

Author: renovate-bot

java-common-protos/pom.xml

@@ -63,7 +63,7 @@
     <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
     <github.global.server>github</github.global.server>
     <site.installationModule>google-iam-parent</site.installationModule>
-    <protobuf.version>3.21.4</protobuf.version>
+    <protobuf.version>3.21.5</protobuf.version>
     <junit.version>4.13.2</junit.version>
     <grpc.version>1.47.0</grpc.version>
     <guava.version>31.0.1-android</guava.version>