deps: update dependency com.google.api:gax-bom to v2.18.0 (#829)

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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) | `2.17.0` -> `2.18.0` | [![age](https://badges.renovateapi.com/packages/maven/com.google.api:gax-bom/2.18.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.api:gax-bom/2.18.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.api:gax-bom/2.18.0/compatibility-slim/2.17.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.api:gax-bom/2.18.0/confidence-slim/2.17.0)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

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

### [`v2.18.0`](https://togithub.com/googleapis/gax-java/blob/HEAD/CHANGELOG.md#&#8203;2180-httpsgithubcomgoogleapisgax-javacomparev2170v2180-2022-05-18)

[Compare Source](https://togithub.com/googleapis/gax-java/compare/v2.17.0...v2.18.0)

##### Features

-   \[REGAPIC] Add support for additional bindings ([#&#8203;1680](https://togithub.com/googleapis/gax-java/issues/1680)) ([59b3699](https://togithub.com/googleapis/gax-java/commit/59b3699b6acbc98c55dc043bf8665b457a0615a9))
-   upgrade graal-sdk to 22.1.0 ([#&#8203;1683](https://togithub.com/googleapis/gax-java/issues/1683)) ([46f899d](https://togithub.com/googleapis/gax-java/commit/46f899de06e60a792f5a6c1dc617673f0f180c00))

##### Bug Fixes

-   **java:** remove conflicting reflection configuration to address UnsupportedFeatureException with GraalVM 22.1.0 ([#&#8203;1682](https://togithub.com/googleapis/gax-java/issues/1682)) ([97c6c8b](https://togithub.com/googleapis/gax-java/commit/97c6c8bfa0d5397e30d3699e92f823e09ee283e6))
-   remove svm dependency ([#&#8203;1679](https://togithub.com/googleapis/gax-java/issues/1679)) ([c1b88e3](https://togithub.com/googleapis/gax-java/commit/c1b88e3788ab866bcc1ba3db94c2998198a0b35e))

##### Dependencies

-   update dependency com.google.api:api-common to 2.2.0 ([#&#8203;1685](https://togithub.com/googleapis/gax-java/issues/1685)) ([a5a316b](https://togithub.com/googleapis/gax-java/commit/a5a316bde322733eb5a80093206eb12b36945580))

</details>

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java-core/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>2.17.0</gax.version>
+    <gax.version>2.18.0</gax.version>
     <google.api-common.version>2.2.0</google.api-common.version>
     <google.common-protos.version>2.8.3</google.common-protos.version>
     <google.iam.version>1.3.4</google.iam.version>