[clang-tidy] LIT test fix for Remark diagnostic

There is a followup fix for a unit test introduced at D102906. The test file was placed into a temp folder and test assumed that it would be visible without the full path specification.

This behaviour can be changed in future and it would be good to specify full path to the file at the test.

Test Plan:
```
ninja check-clang-tools
```

Reviewed By: DmitryPolukhin

Differential Revision: https://reviews.llvm.org/D104021