deps: update autovalue.version to v1.8 (#703)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.auto.value:auto-value-annotations](https://github.com/google/auto) | `1.7.5` -> `1.8` | [![age](https://badges.renovateapi.com/packages/maven/com.google.auto.value:auto-value-annotations/1.8/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.auto.value:auto-value-annotations/1.8/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.auto.value:auto-value-annotations/1.8/compatibility-slim/1.7.5)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.auto.value:auto-value-annotations/1.8/confidence-slim/1.7.5)](https://docs.renovatebot.com/merge-confidence/) |
| [com.google.auto.value:auto-value](https://github.com/google/auto) | `1.7.5` -> `1.8` | [![age](https://badges.renovateapi.com/packages/maven/com.google.auto.value:auto-value/1.8/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.auto.value:auto-value/1.8/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.auto.value:auto-value/1.8/compatibility-slim/1.7.5)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.auto.value:auto-value/1.8/confidence-slim/1.7.5)](https://docs.renovatebot.com/merge-confidence/) |

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google-cloud-bigtable-deps-bom/pom.xml

@@ -71,7 +71,7 @@
   </licenses>
 
   <properties>
-    <autovalue.version>1.7.5</autovalue.version>
+    <autovalue.version>1.8</autovalue.version>
   </properties>
 
   <dependencyManagement>