chore(deps): update dependency com.google.cloud:libraries-bom to v26.8.0 (#2283)

[![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.cloud:libraries-bom](https://cloud.google.com/java/docs/bom) ([source](https://togithub.com/googleapis/java-cloud-bom)) | `26.7.0` -> `26.8.0` | [![age](https://badges.renovateapi.com/packages/maven/com.google.cloud:libraries-bom/26.8.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.cloud:libraries-bom/26.8.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.cloud:libraries-bom/26.8.0/compatibility-slim/26.7.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.cloud:libraries-bom/26.8.0/confidence-slim/26.7.0)](https://docs.renovatebot.com/merge-confidence/) |

---

### Release Notes

<details>
<summary>googleapis/java-cloud-bom</summary>

### [`v26.8.0`](https://togithub.com/googleapis/java-cloud-bom/blob/HEAD/CHANGELOG.md#&#8203;2680-httpsgithubcomgoogleapisjava-cloud-bomcomparev2670v2680-2023-02-13)

[Compare Source](https://togithub.com/googleapis/java-cloud-bom/compare/v26.7.0...v26.8.0)

##### Dependencies

-   update dependency com.google.cloud:google-cloud-bigtable-bom to v2.19.0 ([#&#8203;5817](https://togithub.com/googleapis/java-cloud-bom/issues/5817)) ([cacbbd8](https://togithub.com/googleapis/java-cloud-bom/commit/cacbbd8854cef64615ecf4f14a5699e08c0924e6))

</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/java-spanner).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzNC4xMjUuMSIsInVwZGF0ZWRJblZlciI6IjM0LjEyNS4xIn0=-->

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>26.7.0</version>
+      <version>26.8.0</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>26.7.0</version>
+        <version>26.8.0</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>26.7.0</version>
+        <version>26.8.0</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>