deps: update dependency com.google.cloud:google-cloud-datastore-bom to v2.8.0 (#4499)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.cloud:google-cloud-datastore-bom](https://togithub.com/googleapis/java-datastore) | `2.7.0` -> `2.8.0` | [![age](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-datastore-bom/2.8.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-datastore-bom/2.8.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-datastore-bom/2.8.0/compatibility-slim/2.7.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-datastore-bom/2.8.0/confidence-slim/2.7.0)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

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

### [`v2.8.0`](https://togithub.com/googleapis/java-datastore/blob/HEAD/CHANGELOG.md#&#8203;280-httpsgithubcomgoogleapisjava-datastorecomparev270v280-2022-06-09)

[Compare Source](https://togithub.com/googleapis/java-datastore/compare/v2.7.0...v2.8.0)

##### Features

-   support IN/NOT_IN/NOT_EQUAL operators ([#&#8203;688](https://togithub.com/googleapis/java-datastore/issues/688)) ([f8a84ff](https://togithub.com/googleapis/java-datastore/commit/f8a84ffa6d743501f5cfb71ac271d8a9b764705c))

</details>

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Author: renovate-bot

google-cloud-bom/pom.xml

@@ -352,7 +352,7 @@
       <dependency>
         <groupId>com.google.cloud</groupId>
         <artifactId>google-cloud-datastore-bom</artifactId>
-        <version>2.7.0</version>
+        <version>2.8.0</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>