deps: update dependency com.google.api:gax-bom to v1.66.0 (#483)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.api:gax-bom](https://togithub.com/googleapis/gax-java) | `1.65.1` -> `1.66.0` | [![age](https://badges.renovateapi.com/packages/maven/com.google.api:gax-bom/1.66.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.api:gax-bom/1.66.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.api:gax-bom/1.66.0/compatibility-slim/1.65.1)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.api:gax-bom/1.66.0/confidence-slim/1.65.1)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

<details>
<summary>googleapis/gax-java</summary>

### [`v1.66.0`](https://togithub.com/googleapis/gax-java/blob/master/CHANGELOG.md#&#8203;1660-httpswwwgithubcomgoogleapisgax-javacomparev1651v1660-2021-06-24)

[Compare Source](https://togithub.com/googleapis/gax-java/compare/v1.65.1...v1.66.0)

##### Features

-   make ApiTracer internal API ([#&#8203;1414](https://www.github.com/googleapis/gax-java/issues/1414)) ([e3e8462](https://www.github.com/googleapis/gax-java/commit/e3e8462a2f9e866480ec2106dc59555d41ea4bb5))

##### [1.65.1](https://www.github.com/googleapis/gax-java/compare/v1.65.0...v1.65.1) (2021-06-08)

##### Bug Fixes

-   fix grammar in StubSetting comment ([#&#8203;1397](https://www.github.com/googleapis/gax-java/issues/1397)) ([b015910](https://www.github.com/googleapis/gax-java/commit/b0159102b52fd4b778a9bde15b1acd2e9fa6958e))

</details>

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Author: renovate-bot

pom.xml

@@ -151,7 +151,7 @@
     <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
     <github.global.server>github</github.global.server>
     <site.installationModule>google-cloud-core-parent</site.installationModule>
-    <gax.version>1.65.1</gax.version>
+    <gax.version>1.66.0</gax.version>
     <google.api-common.version>1.10.4</google.api-common.version>
     <google.common-protos.version>2.3.2</google.common-protos.version>
     <google.iam.version>1.0.14</google.iam.version>