Bump com.google.cloud:google-cloud-spanner in /modules/gcloud

Bumps [com.google.cloud:google-cloud-spanner](https://github.com/googleapis/java-spanner) from 6.38.2 to 6.42.3.
- [Release notes](https://github.com/googleapis/java-spanner/releases)
- [Changelog](https://github.com/googleapis/java-spanner/blob/main/CHANGELOG.md)
- [Commits](googleapis/java-spanner@v6.38.2...v6.42.3)

---
updated-dependencies:
- dependency-name: com.google.cloud:google-cloud-spanner
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]

modules/gcloud/build.gradle

@@ -6,7 +6,7 @@ dependencies {
     testImplementation 'com.google.cloud:google-cloud-datastore:2.14.2'
     testImplementation 'com.google.cloud:google-cloud-firestore:3.9.3'
     testImplementation 'com.google.cloud:google-cloud-pubsub:1.123.8'
-    testImplementation 'com.google.cloud:google-cloud-spanner:6.38.2'
+    testImplementation 'com.google.cloud:google-cloud-spanner:6.42.3'
     testImplementation 'com.google.cloud:google-cloud-bigtable:2.20.3'
     testImplementation 'org.assertj:assertj-core:3.24.2'
 }