deps: update dependency com.google.cloud:google-cloud-core to v2.8.13 (#1288)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.cloud:google-cloud-core](https://togithub.com/googleapis/java-core) | `2.8.12` -> `2.8.13` | [![age](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-core/2.8.13/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-core/2.8.13/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-core/2.8.13/compatibility-slim/2.8.12)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-core/2.8.13/confidence-slim/2.8.12)](https://docs.renovatebot.com/merge-confidence/) |

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Author: renovate-bot

samples/install-without-bom/pom.xml

@@ -80,7 +80,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-core</artifactId>
-      <version>2.8.12</version>
+      <version>2.8.13</version>
       <classifier>tests</classifier>
     </dependency>
     <dependency>

samples/snapshot/pom.xml

@@ -79,7 +79,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-core</artifactId>
-      <version>2.8.12</version>
+      <version>2.8.13</version>
       <classifier>tests</classifier>
     </dependency>
     <dependency>

samples/snippets/pom.xml

@@ -94,7 +94,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-core</artifactId>
-      <version>2.8.12</version>
+      <version>2.8.13</version>
       <classifier>tests</classifier>
     </dependency>
     <!-- [END_EXCLUDE] -->