chore(deps): update dependency com.google.cloud:google-cloud-firestore to v3.15.7 (#1494)

* chore(deps): update dependency com.google.cloud:google-cloud-firestore to v3.15.7

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: renovate-bot

README.md

@@ -42,7 +42,7 @@ If you are using Maven without the BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-firestore</artifactId>
-  <version>3.15.6</version>
+  <version>3.15.7</version>
 </dependency>
 
 ```

samples/install-without-bom/pom.xml

@@ -30,7 +30,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-firestore</artifactId>
-      <version>3.15.6</version>
+      <version>3.15.7</version>
     </dependency>
     <!-- [END firestore_install_without_bom] -->
 

samples/snapshot/pom.xml

@@ -29,7 +29,7 @@
     <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-firestore</artifactId>
-      <version>3.15.6</version>
+      <version>3.15.7</version>
     </dependency>
 
     <dependency>