deps: update dependency com.google.cloud:google-cloud-firestore-bom to v3.9.6 (#5944)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [com.google.cloud:google-cloud-firestore-bom](https://togithub.com/googleapis/java-firestore) | `3.9.4` -> `3.9.6` | [![age](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-firestore-bom/3.9.6/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-firestore-bom/3.9.6/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-firestore-bom/3.9.6/compatibility-slim/3.9.4)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/maven/com.google.cloud:google-cloud-firestore-bom/3.9.6/confidence-slim/3.9.4)](https://docs.renovatebot.com/merge-confidence/) |

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### ⚠ Dependency Lookup Warnings ⚠

Warnings were logged while processing this repo. Please check the Dependency Dashboard for more information.

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### Release Notes

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

### [`v3.9.6`](https://togithub.com/googleapis/java-firestore/blob/HEAD/CHANGELOG.md#&#8203;396-httpsgithubcomgoogleapisjava-firestorecomparev395v396-2023-04-26)

[Compare Source](https://togithub.com/googleapis/java-firestore/compare/v3.9.5...v3.9.6)

##### Dependencies

-   Update dependency org.junit.vintage:junit-vintage-engine to v5.9.3 ([#&#8203;1275](https://togithub.com/googleapis/java-firestore/issues/1275)) ([1f32893](https://togithub.com/googleapis/java-firestore/commit/1f328937a9e1a1ed5b76400a65580ee79562d1f2))

### [`v3.9.5`](https://togithub.com/googleapis/java-firestore/blob/HEAD/CHANGELOG.md#&#8203;395-httpsgithubcomgoogleapisjava-firestorecomparev394v395-2023-04-25)

[Compare Source](https://togithub.com/googleapis/java-firestore/compare/v3.9.4...v3.9.5)

##### Dependencies

-   Update dependency com.google.cloud:google-cloud-shared-dependencies to v3.8.0 ([#&#8203;1268](https://togithub.com/googleapis/java-firestore/issues/1268)) ([8a92dc9](https://togithub.com/googleapis/java-firestore/commit/8a92dc915ae30c339a90d0e2fe1afb2cbbb0aa3f))

</details>

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Author: renovate-bot

google-cloud-bom/pom.xml

@@ -200,7 +200,7 @@
       <dependency>
         <groupId>com.google.cloud</groupId>
         <artifactId>google-cloud-firestore-bom</artifactId>
-        <version>3.9.4</version>
+        <version>3.9.6</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>