deps: update dependency com.google.protobuf:protobuf-java-util to v3.15.5 (#559)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| com.google.protobuf:protobuf-java-util | `3.15.3` -> `3.15.5` | [![age](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-java-util/3.15.5/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-java-util/3.15.5/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-java-util/3.15.5/compatibility-slim/3.15.3)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.protobuf:protobuf-java-util/3.15.5/confidence-slim/3.15.3)](https://docs.renovatebot.com/merge-confidence/) |

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samples/install-without-bom/pom.xml

@@ -75,7 +75,7 @@
     <dependency>
       <groupId>com.google.protobuf</groupId>
       <artifactId>protobuf-java-util</artifactId>
-      <version>3.15.3</version>
+      <version>3.15.5</version>
     </dependency>
     <dependency>
       <groupId>com.google.cloud</groupId>

samples/snapshot/pom.xml

@@ -61,7 +61,7 @@
     <dependency>
       <groupId>com.google.protobuf</groupId>
       <artifactId>protobuf-java-util</artifactId>
-      <version>3.15.3</version>
+      <version>3.15.5</version>
     </dependency>
 
     <dependency>

samples/snippets/pom.xml

@@ -72,7 +72,7 @@
     <dependency>
       <groupId>com.google.protobuf</groupId>
       <artifactId>protobuf-java-util</artifactId>
-      <version>3.15.3</version>
+      <version>3.15.5</version>
     </dependency>
 
     <dependency>