chore(deps): update dependency com.google.cloud:libraries-bom to v21 (#850)

[![WhiteSource 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.cloud:libraries-bom](https://github.com/GoogleCloudPlatform/cloud-opensource-java) | `20.9.0` -> `21.0.0` | [![age](https://badges.renovateapi.com/packages/maven/com.google.cloud:libraries-bom/21.0.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.cloud:libraries-bom/21.0.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.cloud:libraries-bom/21.0.0/compatibility-slim/20.9.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.cloud:libraries-bom/21.0.0/confidence-slim/20.9.0)](https://docs.renovatebot.com/merge-confidence/) |

---

### Configuration

📅 **Schedule**: At any time (no schedule defined).

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

♻ **Rebasing**: Renovate will not automatically rebase this PR, because other commits have been found.

🔕 **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 [WhiteSource Renovate](https://renovate.whitesourcesoftware.com). View repository job log [here](https://app.renovatebot.com/dashboard#github/googleapis/java-asset).

Author: renovate-bot

asset/pom.xml

@@ -29,7 +29,7 @@
       <dependency>
         <groupId>com.google.cloud</groupId>
         <artifactId>libraries-bom</artifactId>
-        <version>20.9.0</version>
+        <version>21.0.0</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>