chore(deps): update dependency com.google.cloud:google-cloud-kms to v2.6.4 (#846)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.cloud:google-cloud-kms](https://github.com/googleapis/java-kms) | `2.6.3` -> `2.6.4` | [![age](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-kms/2.6.4/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-kms/2.6.4/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-kms/2.6.4/compatibility-slim/2.6.3)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-kms/2.6.4/confidence-slim/2.6.3)](https://docs.renovatebot.com/merge-confidence/) |

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java-kms/README.md

@@ -42,7 +42,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-kms</artifactId>
-  <version>2.6.3</version>
+  <version>2.6.4</version>
 </dependency>
 
 ```

java-kms/samples/install-without-bom/pom.xml

@@ -29,7 +29,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-kms</artifactId>
-      <version>2.6.3</version>
+      <version>2.6.4</version>
     </dependency>
     <!-- [END cloudkms_install_without_bom] -->