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### _Why are the changes needed?_
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Fix broken links in the doc and PULL_REQUEST_TEMPLATE.

### _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

- [x] [Run test](https://kyuubi.readthedocs.io/en/latest/tools/testing.html#running-tests

) locally before make a pull request

Closes #912 from BoyangYue/testing.

Closes #912

239ad681 [Yue Boyang] Fix broken links in the doc and PULL_REQUEST_TEMPLATE
Authored-by: Yue Boyang <boyang.yue@student.unimelb.edu.au>
Signed-off-by: Cheng Pan <chengpan@apache.org>