### _Why are the changes needed?_
### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible
- [ ] Add screenshots for manual tests if appropriate
- [ ] [Run test](https://kyuubi.apache.org/docs/latest/develop_tools/testing.html#running-tests) locally before make a pull request
Closes#3207 from deadwind4/flink-default-version.
Closes#3206
4c9b5d6c [Luning Wang] Fix test case to fit flink 1.14 and 1.15
09c854e2 [Luning Wang] change sql-client.jar name to fit flink 1.15
eef06d1e [Luning Wang] change the suffix to fit 1.15
93fb44f4 [Luning Wang] Comment out cross validation
8ea10218 [Luning Wang] Fix cross validation
a5e5cdb9 [Luning Wang] Fix github CI Flink version
1ee8a5d9 [Luning Wang] [KYUUBI #3206] Change Flink default version to 1.15
Authored-by: Luning Wang <wang4luning@gmail.com>
Signed-off-by: Cheng Pan <chengpan@apache.org>