spark: update compiler source/target from Java 8 to Java 11

- Fix inconsistency between maven.compiler.source/target (1.8) and
  surefire JVM args (Java 9+ module flags like --add-opens)
- Update to Java 11 to match CI environment (GitHub Actions uses Java 11)
- Docker environment uses Java 17 which is also compatible
- Java 11+ is required for the --add-opens/--add-exports flags used
  in the surefire configuration

test/java/spark/pom.xml

@@ -14,8 +14,8 @@
 
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <maven.compiler.source>1.8</maven.compiler.source>
-        <maven.compiler.target>1.8</maven.compiler.target>
+        <maven.compiler.source>11</maven.compiler.source>
+        <maven.compiler.target>11</maven.compiler.target>
         <spark.version>3.5.0</spark.version>
         <hadoop.version>3.3.6</hadoop.version>
         <scala.binary.version>2.12</scala.binary.version>