deps: update dependency com.google.api.grpc:proto-google-cloud-spanner-executor-v1 to v1.4.0 (#2395)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.api.grpc:proto-google-cloud-spanner-executor-v1](https://togithub.com/googleapis/java-spanner/proto-google-cloud-spanner-executor-v1) ([source](https://togithub.com/googleapis/java-spanner)) | `1.3.0` -> `1.4.0` | [![age](https://badges.renovateapi.com/packages/maven/com.google.api.grpc:proto-google-cloud-spanner-executor-v1/1.4.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.api.grpc:proto-google-cloud-spanner-executor-v1/1.4.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.api.grpc:proto-google-cloud-spanner-executor-v1/1.4.0/compatibility-slim/1.3.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.api.grpc:proto-google-cloud-spanner-executor-v1/1.4.0/confidence-slim/1.3.0)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

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

### [`v1.4.0`](https://togithub.com/googleapis/java-spanner/compare/1.3.0...1.4.0)

[Compare Source](https://togithub.com/googleapis/java-spanner/compare/1.3.0...1.4.0)

</details>

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README.md

@@ -50,7 +50,7 @@ If you are using Maven without the BOM, add this to your dependencies:
 If you are using Gradle 5.x or later, add this to your dependencies:
 
 ```Groovy
-implementation platform('com.google.cloud:libraries-bom:26.12.0')
+implementation platform('com.google.cloud:libraries-bom:26.13.0')
 
 implementation 'com.google.cloud:google-cloud-spanner'
 ```

google-cloud-spanner-executor/pom.xml

@@ -81,7 +81,7 @@
     <dependency>
       <groupId>com.google.api.grpc</groupId>
       <artifactId>proto-google-cloud-spanner-executor-v1</artifactId>
-      <version>1.3.0</version>
+      <version>1.4.0</version>
     </dependency>
     <dependency>
       <groupId>com.google.guava</groupId>