Change vdiff log message level of missing target rows to Warning since it is confusing to users (and not useful) to see the message on the console when running vdiff during a workflow

Signed-off-by: Rohit Nayak <rohit@planetscale.com>

go/vt/wrangler/vdiff.go

@@ -806,7 +806,7 @@ func (td *tableDiffer) diff(ctx context.Context, wr *Wrangler) (*DiffReport, err
 		if targetRow == nil {
 			// no more rows from the target
 			// we know we have rows from source, drain, update count
-			wr.Logger().Errorf("Draining extra row(s) found on the source starting with: %v", sourceRow)
+			wr.Logger().Warningf("Draining extra row(s) found on the source starting with: %v", sourceRow)
 			count, err := sourceExecutor.drain(ctx)
 			if err != nil {
 				return nil, err