fix(spanner): unflake unit tests

Author: sakthivelmanii

README.md

@@ -31,7 +31,7 @@ If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file:
     <groupId>com.google.cloud</groupId>
     <artifactId>google-cloud-spanner</artifactId>
   </dependency>
-
+</dependencies>
 ```
 
 If you are using Maven without the BOM, add this to your dependencies: