build(deps): update dependency org.apache.maven.plugins:maven-compiler-plugin to v3.15.0

Author: renovate-bot

gapic-generator-java/pom.xml

@@ -107,7 +107,7 @@
       </plugin>
       <plugin>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.13.0</version>
+        <version>3.15.0</version>
         <configuration>
           <source>8</source>
           <target>8</target>