[SPARK-37769][SQL][FOLLOWUP] Add UTF8String import in FileScanRDD.scala

### What changes were proposed in this pull request?
This PR fixes the import missing. Logical conflict between apache#35068 and apache#35055.

### Why are the changes needed?

To fix up the complication.

### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?
CI should test it out in compliation.

Closes apache#35245 from HyukjinKwon/SPARK-37896.

Authored-by: Hyukjin Kwon <[email protected]>
Signed-off-by: Hyukjin Kwon <[email protected]>

Author: HyukjinKwon

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/FileScanRDD.scala

@@ -34,6 +34,7 @@ import org.apache.spark.sql.execution.datasources.FileFormat._
 import org.apache.spark.sql.execution.vectorized.ConstantColumnVector
 import org.apache.spark.sql.types.{LongType, StringType, StructType}
 import org.apache.spark.sql.vectorized.ColumnarBatch
+import org.apache.spark.unsafe.types.UTF8String
 import org.apache.spark.util.NextIterator
 
 /**