[SPARK-44086][SQL][TESTS] Move DataFrameFunctionsSuite to sql - slow

### What changes were proposed in this pull request?
Move `DataFrameFunctionsSuite` to `sql - slow`

### Why are the changes needed?
1, recently `DataFrameFunctionsSuite` is frequently updated for the new functions, while `sql - other` is quite flaky and it's likely to get stuck or failed before `DataFrameFunctionsSuite` is actually tested (see 61a195d and 37f9bea), so it is hard for the reviewers to judge whether all related tests pass;
2, `sql - other` is actually much slower than `sql - slow`, so I think it is fine to move a suite to `sql - slow`;

### Does this PR introduce _any_ user-facing change?
no, test-only

### How was this patch tested?
updated GA

Closes #41643 from zhengruifeng/sql_test_move_dfsuite.

Authored-by: Ruifeng Zheng <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: zhengruifeng

sql/core/src/test/scala/org/apache/spark/sql/DataFrameFunctionsSuite.scala

@@ -36,10 +36,12 @@ import org.apache.spark.sql.functions._
 import org.apache.spark.sql.internal.SQLConf
 import org.apache.spark.sql.test.SharedSparkSession
 import org.apache.spark.sql.types._
+import org.apache.spark.tags.ExtendedSQLTest
 
 /**
  * Test suite for functions in [[org.apache.spark.sql.functions]].
  */
+@ExtendedSQLTest
 class DataFrameFunctionsSuite extends QueryTest with SharedSparkSession {
   import testImplicits._