deps: update dependency com.google.cloud:google-cloud-spanner-bom to v6.71.0 (#1672)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.cloud:google-cloud-spanner-bom](https://togithub.com/googleapis/java-spanner) | `6.70.0` -> `6.71.0` | [![age](https://developer.mend.io/api/mc/badges/age/maven/com.google.cloud:google-cloud-spanner-bom/6.71.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://developer.mend.io/api/mc/badges/adoption/maven/com.google.cloud:google-cloud-spanner-bom/6.71.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://developer.mend.io/api/mc/badges/compatibility/maven/com.google.cloud:google-cloud-spanner-bom/6.70.0/6.71.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://developer.mend.io/api/mc/badges/confidence/maven/com.google.cloud:google-cloud-spanner-bom/6.70.0/6.71.0?slim=true)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

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

### [`v6.71.0`](https://togithub.com/googleapis/java-spanner/blob/HEAD/CHANGELOG.md#6710-2024-07-03)

[Compare Source](https://togithub.com/googleapis/java-spanner/compare/v6.70.0...v6.71.0)

##### Features

-   Include thread name in traces ([#&#8203;3173](https://togithub.com/googleapis/java-spanner/issues/3173)) ([92b1e07](https://togithub.com/googleapis/java-spanner/commit/92b1e079e6093bc4a2e7b458c1bbe0f62a0fada9))
-   Support multiplexed sessions for RO transactions ([#&#8203;3141](https://togithub.com/googleapis/java-spanner/issues/3141)) ([2b8e9ed](https://togithub.com/googleapis/java-spanner/commit/2b8e9ededc1ea1a5e8d4f90083f2cf862fcc198a))

</details>

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Author: renovate-bot

pom.xml

@@ -62,7 +62,7 @@
       <dependency>
         <groupId>com.google.cloud</groupId>
         <artifactId>google-cloud-spanner-bom</artifactId>
-        <version>6.70.0</version>
+        <version>6.71.0</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>

samples/spring-data-jdbc/pom.xml

@@ -30,7 +30,7 @@
       <dependency>
         <groupId>com.google.cloud</groupId>
         <artifactId>google-cloud-spanner-bom</artifactId>
-        <version>6.70.0</version>
+        <version>6.71.0</version>
         <scope>import</scope>
         <type>pom</type>
       </dependency>