*: refine github templates

[xhebox]

Signed-off-by: xhe [email protected]

What problem does this PR solve?

As title. So that I have checkboxes in PR.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has configuration change
• Has HTTP API interfaces change (Don't forget to add the declarative for API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tidb-ansible:
• Need to cherry-pick to the release branch

Release note