chore(deps): update dependency com.google.cloud:google-cloud-spanner-jdbc to v1.18.3 (#317)

Author: renovate-bot

samples/install-without-bom/pom.xml

@@ -29,7 +29,7 @@
  <dependency>
  <groupId>com.google.cloud</groupId>
  <artifactId>google-cloud-spanner-jdbc</artifactId>
- <version>1.18.2</version>
+ <version>1.18.3</version>
  </dependency>
  <!-- [END spanner-jdbc_install_without_bom] -->