deps: update dependency com.google.cloud:google-cloud-spanner-bom to v6.50.0 (#1386)

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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) | `6.49.0` -> `6.50.0` | [![age](https://developer.mend.io/api/mc/badges/age/maven/com.google.cloud:google-cloud-spanner-bom/6.50.0?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/6.50.0?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/6.49.0/6.50.0?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/6.49.0/6.50.0?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>

### [`v6.50.0`](https://togithub.com/googleapis/java-spanner/blob/HEAD/CHANGELOG.md#6500-2023-10-09)

[Compare Source](https://togithub.com/googleapis/java-spanner/compare/v6.49.0...v6.50.0)

##### Features

-   Support setting core pool size for async API in system property ([#&#8203;2632](https://togithub.com/googleapis/java-spanner/issues/2632)) ([e51c55d](https://togithub.com/googleapis/java-spanner/commit/e51c55d332bacb9d174a24b0d842b2cba4762db8)), closes [#&#8203;2631](https://togithub.com/googleapis/java-spanner/issues/2631)

##### Dependencies

-   Update dependency com.google.cloud:google-cloud-trace to v2.24.0 ([#&#8203;2577](https://togithub.com/googleapis/java-spanner/issues/2577)) ([311c2ad](https://togithub.com/googleapis/java-spanner/commit/311c2ad97311490893f3abf4da5fe4d511c445dd))

</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>6.49.0</version>
+        <version>6.50.0</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>