deps: update dependency com.google.api.grpc:proto-google-iam-v1 to v1.8.0 (#1082)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.api.grpc:proto-google-iam-v1](https://togithub.com/googleapis/gapic-generator-java) | `1.7.0` -> `1.8.0` | [![age](https://badges.renovateapi.com/packages/maven/com.google.api.grpc:proto-google-iam-v1/1.8.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.api.grpc:proto-google-iam-v1/1.8.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.api.grpc:proto-google-iam-v1/1.8.0/compatibility-slim/1.7.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.api.grpc:proto-google-iam-v1/1.8.0/confidence-slim/1.7.0)](https://docs.renovatebot.com/merge-confidence/) |

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pom.xml

@@ -154,7 +154,7 @@
     <gax.version>2.21.0</gax.version>
     <google.api-common.version>2.4.0</google.api-common.version>
     <google.common-protos.version>2.13.0</google.common-protos.version>
-    <google.iam.version>1.7.0</google.iam.version>
+    <google.iam.version>1.8.0</google.iam.version>
     <google.auth.version>1.14.0</google.auth.version>
     <google.api.version>2.1.2</google.api.version>
     <google.http.version>1.42.3</google.http.version>