fix(deps): update dependency com.google.protobuf:protobuf-bom to v3.21.12 (#1116)

[![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)) | `3.21.10` -> `3.21.12` | [![age](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.12/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.12/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.12/compatibility-slim/3.21.10)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-bom/3.21.12/confidence-slim/3.21.10)](https://docs.renovatebot.com/merge-confidence/) |

---

### ⚠ Dependency Lookup Warnings ⚠

Warnings were logged while processing this repo. Please check the Dependency Dashboard for more information.

---

### Release Notes

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

### [`v3.21.12`](https://togithub.com/protocolbuffers/protobuf/compare/v3.21.11...v3.21.12)

[Compare Source](https://togithub.com/protocolbuffers/protobuf/compare/v3.21.11...v3.21.12)

### [`v3.21.11`](https://togithub.com/protocolbuffers/protobuf/compare/v3.21.10...v3.21.11)

[Compare Source](https://togithub.com/protocolbuffers/protobuf/compare/v3.21.10...v3.21.11)

</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, check this box

---

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/gapic-generator-java).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzNC4yNC4wIiwidXBkYXRlZEluVmVyIjoiMzQuMjQuMCJ9-->

Author: renovate-bot

gapic-generator-java-pom-parent/pom.xml

@@ -30,7 +30,7 @@
     <google.auth.version>1.14.0</google.auth.version>
     <gson.version>2.10</gson.version>
     <guava.version>31.1-jre</guava.version>
-    <protobuf.version>3.21.10</protobuf.version>
+    <protobuf.version>3.21.12</protobuf.version>
   </properties>
 
   <developers>