deps: updated dependency of google-cloud-bigtable-bom (#6981)

* deps: updated dependency of google-cloud-bigtable-bom

* 2.56.0 is the latest

---------

Co-authored-by: Tomo Suzuki <suztomo@gmail.com>

Author: sarthakbhutani

google-cloud-bom/pom.xml

@@ -186,7 +186,7 @@
       <dependency>
         <groupId>com.google.cloud</groupId>
         <artifactId>google-cloud-bigtable-bom</artifactId>
-        <version>2.54.0</version>
+        <version>2.56.0</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>