deps: update dependency com.google.cloud:google-cloud-spanner-bom to v6.40.1 (#1207)

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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) | `6.38.2` -> `6.40.1` | [![age](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-spanner-bom/6.40.1/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-spanner-bom/6.40.1/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-spanner-bom/6.40.1/compatibility-slim/6.38.2)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-spanner-bom/6.40.1/confidence-slim/6.38.2)](https://docs.renovatebot.com/merge-confidence/) |

---

### Release Notes

<details>
<summary>googleapis/java-spanner</summary>

### [`v6.40.1`](https://togithub.com/googleapis/java-spanner/blob/HEAD/CHANGELOG.md#&#8203;6401-httpsgithubcomgoogleapisjava-spannercomparev6400v6401-2023-04-17)

[Compare Source](https://togithub.com/googleapis/java-spanner/compare/v6.40.0...v6.40.1)

##### Dependencies

-   Update dependency com.google.cloud:google-cloud-monitoring to v3.16.0 ([#&#8203;2383](https://togithub.com/googleapis/java-spanner/issues/2383)) ([5d5c33a](https://togithub.com/googleapis/java-spanner/commit/5d5c33ae7c01e10112c72777f202187a50b55ac3))
-   Update dependency com.google.cloud:google-cloud-trace to v2.15.0 ([#&#8203;2384](https://togithub.com/googleapis/java-spanner/issues/2384)) ([6b4ce1f](https://togithub.com/googleapis/java-spanner/commit/6b4ce1fc7ffd837fab6250e36269589d95f5b8c6))

### [`v6.40.0`](https://togithub.com/googleapis/java-spanner/blob/HEAD/CHANGELOG.md#&#8203;6400-httpsgithubcomgoogleapisjava-spannercomparev6390v6400-2023-04-14)

[Compare Source](https://togithub.com/googleapis/java-spanner/compare/v6.39.0...v6.40.0)

##### Features

-   Savepoints ([#&#8203;2278](https://togithub.com/googleapis/java-spanner/issues/2278)) ([b02f584](https://togithub.com/googleapis/java-spanner/commit/b02f58435b97346cc8e08a96635affe8383981bb))

##### Performance Improvements

-   Remove custom transport executor ([#&#8203;2366](https://togithub.com/googleapis/java-spanner/issues/2366)) ([e27dbe5](https://togithub.com/googleapis/java-spanner/commit/e27dbe5f58229dab208eeeed44d53e741700c814))

##### Dependencies

-   Update dependency com.google.cloud:google-cloud-shared-dependencies to v3.7.0 ([#&#8203;2377](https://togithub.com/googleapis/java-spanner/issues/2377)) ([40402af](https://togithub.com/googleapis/java-spanner/commit/40402af54f94f16619d018e252181db29ae6855e))
-   Update dependency org.graalvm.buildtools:junit-platform-native to v0.9.21 ([#&#8203;2379](https://togithub.com/googleapis/java-spanner/issues/2379)) ([ae7262d](https://togithub.com/googleapis/java-spanner/commit/ae7262d37391c0ec2fee1dcbb24899e4fa16ae17))
-   Update dependency org.graalvm.buildtools:native-maven-plugin to v0.9.21 ([#&#8203;2380](https://togithub.com/googleapis/java-spanner/issues/2380)) ([0cb159e](https://togithub.com/googleapis/java-spanner/commit/0cb159efc97f02b42f064244e3812a0fd3d82db6))

### [`v6.39.0`](https://togithub.com/googleapis/java-spanner/blob/HEAD/CHANGELOG.md#&#8203;6390-httpsgithubcomgoogleapisjava-spannercomparev6382v6390-2023-04-11)

[Compare Source](https://togithub.com/googleapis/java-spanner/compare/v6.38.2...v6.39.0)

##### Features

-   Capture stack trace for session checkout is now optional ([#&#8203;2350](https://togithub.com/googleapis/java-spanner/issues/2350)) ([6b6427a](https://togithub.com/googleapis/java-spanner/commit/6b6427a25af25fde944dfc1dd4bf6a6463682caf))

</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>6.38.2</version>
+        <version>6.40.1</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>