deps: update gax.version to v2.7.1 (#544)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.api:gax-grpc](https://togithub.com/googleapis/gax-java) | `2.7.0` -> `2.7.1` | [![age](https://badges.renovateapi.com/packages/maven/com.google.api:gax-grpc/2.7.1/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.api:gax-grpc/2.7.1/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.api:gax-grpc/2.7.1/compatibility-slim/2.7.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.api:gax-grpc/2.7.1/confidence-slim/2.7.0)](https://docs.renovatebot.com/merge-confidence/) |
| [com.google.api:gax-bom](https://togithub.com/googleapis/gax-java) | `2.7.0` -> `2.7.1` | [![age](https://badges.renovateapi.com/packages/maven/com.google.api:gax-bom/2.7.1/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.api:gax-bom/2.7.1/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.api:gax-bom/2.7.1/compatibility-slim/2.7.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.api:gax-bom/2.7.1/confidence-slim/2.7.0)](https://docs.renovatebot.com/merge-confidence/) |

---

### Release Notes

<details>
<summary>googleapis/gax-java (com.google.api:gax-grpc)</summary>

### [`v2.7.1`](https://togithub.com/googleapis/gax-java/blob/master/CHANGELOG.md#&#8203;271-httpswwwgithubcomgoogleapisgax-javacomparev270v271-2021-12-02)

[Compare Source](https://togithub.com/googleapis/gax-java/compare/v2.7.0...v2.7.1)

</details>

<details>
<summary>googleapis/gax-java (com.google.api:gax-bom)</summary>

</details>

---

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first-party-dependencies/pom.xml

@@ -56,7 +56,7 @@
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <site.installationModule>${project.artifactId}</site.installationModule>
     <grpc.version>1.42.1</grpc.version>
-    <gax.version>2.7.0</gax.version>
+    <gax.version>2.7.1</gax.version>
     <grpc-gcp.version>1.1.0</grpc-gcp.version>
     <guava.version>31.0.1-jre</guava.version>
     <protobuf.version>3.19.1</protobuf.version>