See https://github.com/go-gitea/gitea/pull/27718#issuecomment-1773743014
. Add a test to ensure its behavior.
Why this test uses `ProjectBoardID=0`? Because in `SearchOptions`,
`ProjectBoardID=0` means what it is. But in `IssueOptions`,
`ProjectBoardID=0` means there is no condition, and
`ProjectBoardID=db.NoConditionID` means the board ID = 0.
It's really confusing. Probably it's better to separate the db search
engine and the other issue search code. It's really two different
systems. As far as I can see, `IssueOptions` is not necessary for most
of the code, which has very simple issue search conditions.
