deps: update dependency com.google.cloud:google-cloud-shared-dependencies to v3.21.0 (googleapis#1854)

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

Author: renovate-bot

pom.xml

@@ -61,7 +61,7 @@
  <dependency>
  <groupId>com.google.cloud</groupId>
  <artifactId>google-cloud-shared-dependencies</artifactId>
- <version>3.20.0</version>
+ <version>3.21.0</version>
  <type>pom</type>
  <scope>import</scope>
  </dependency>