build(deps): update dependency com.google.cloud:google-cloud-shared-config to v0.9.3 (#390)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [com.google.cloud:google-cloud-shared-config](https://togithub.com/googleapis/java-shared-config) | patch | `0.9.2` -> `0.9.3` |

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### Release Notes

<details>
<summary>googleapis/java-shared-config</summary>

### [`v0.9.3`](https://togithub.com/googleapis/java-shared-config/blob/master/CHANGELOG.md#&#8203;093-httpswwwgithubcomgoogleapisjava-shared-configcomparev092v093-2020-10-15)

[Compare Source](https://togithub.com/googleapis/java-shared-config/compare/v0.9.2...v0.9.3)

</details>

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google-cloud-pubsub-bom/pom.xml

@@ -8,7 +8,7 @@
   <parent>
     <groupId>com.google.cloud</groupId>
     <artifactId>google-cloud-shared-config</artifactId>
-    <version>0.9.2</version>
+    <version>0.9.3</version>
   </parent>
 
   <name>Google Cloud pubsub BOM</name>

pom.xml

@@ -14,7 +14,7 @@
   <parent>
     <groupId>com.google.cloud</groupId>
     <artifactId>google-cloud-shared-config</artifactId>
-    <version>0.9.2</version>
+    <version>0.9.3</version>
   </parent>
 
   <developers>