chore(deps): update dependency com.google.cloud:libraries-bom to v26.21.0 (#2561)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.cloud:libraries-bom](https://cloud.google.com/java/docs/bom) ([source](https://togithub.com/googleapis/java-cloud-bom)) | `26.20.0` -> `26.21.0` | [![age](https://developer.mend.io/api/mc/badges/age/maven/com.google.cloud:libraries-bom/26.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://developer.mend.io/api/mc/badges/adoption/maven/com.google.cloud:libraries-bom/26.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://developer.mend.io/api/mc/badges/compatibility/maven/com.google.cloud:libraries-bom/26.20.0/26.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://developer.mend.io/api/mc/badges/confidence/maven/com.google.cloud:libraries-bom/26.20.0/26.21.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) |

---

### Release Notes

<details>
<summary>googleapis/java-cloud-bom (com.google.cloud:libraries-bom)</summary>

### [`v26.21.0`](https://togithub.com/googleapis/java-cloud-bom/blob/HEAD/CHANGELOG.md#26210-2023-08-01)

[Compare Source](https://togithub.com/googleapis/java-cloud-bom/compare/v26.20.0...v26.21.0)

##### Bug Fixes

-   Use Guava v32.1.2 to resolve gradle metadata issue ([#&#8203;6140](https://togithub.com/googleapis/java-cloud-bom/issues/6140)) ([d4cf969](https://togithub.com/googleapis/java-cloud-bom/commit/d4cf9697766e5ac11927bb1e10bf4d5c2a149f63))

##### Dependencies

-   update dependency com.google.cloud:google-cloud-firestore-bom to v3.13.8 ([#&#8203;6138](https://togithub.com/googleapis/java-cloud-bom/issues/6138)) ([2c47308](https://togithub.com/googleapis/java-cloud-bom/commit/2c4730820ed9993690fafe4184dece137a46a4c0))

</details>

---

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Author: renovate-bot

README.md

@@ -19,7 +19,7 @@ If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file:
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>libraries-bom</artifactId>
-      <version>26.20.0</version>
+      <version>26.21.0</version>
       <type>pom</type>
       <scope>import</scope>
     </dependency>

samples/native-image/pom.xml

@@ -28,7 +28,7 @@
       <dependency>
         <groupId>com.google.cloud</groupId>
         <artifactId>libraries-bom</artifactId>
-        <version>26.20.0</version>
+        <version>26.21.0</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>

samples/snippets/pom.xml

@@ -33,7 +33,7 @@
       <dependency>
         <groupId>com.google.cloud</groupId>
         <artifactId>libraries-bom</artifactId>
-        <version>26.20.0</version>
+        <version>26.21.0</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>