[SPARK-36147][SQL] Warn if less files visible after stats write in Ba…

…sicWriteStatsTracker

### What changes were proposed in this pull request?

This log should at least be WARN not INFO (in org/apache/spark/sql/execution/datasources/BasicWriteStatsTracker.scala )
"Expected $numSubmittedFiles files, but only saw $numFiles."

### Why are the changes needed?

INFO logs don't indicate possible issue but WARN logs should

### Does this PR introduce any user-facing change?

Yes, Log level changed.

### How was this patch tested?

manual, trivial change

Closes #33332 from tooptoop4/warn.

Authored-by: tooptoop4 <33283496+tooptoop4@users.noreply.github.com>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>

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

@@ -169,7 +169,7 @@ class BasicWriteTaskStatsTracker(
     }
 
     if (numSubmittedFiles != numFiles) {
-      logInfo(s"Expected $numSubmittedFiles files, but only saw $numFiles. " +
+      logWarning(s"Expected $numSubmittedFiles files, but only saw $numFiles. " +
         "This could be due to the output format not writing empty files, " +
         "or files being not immediately visible in the filesystem.")
     }