Re: [PATCH v2] t7110: replace `test -f` with `test_path_is_*` helpers

> From: matteobagnolini <matteobagnolini2003@gmail.com>
> 
> `test -f` and `! test -f` do not provide clear error messages when they fail.
> To enhance debuggability, use `test_path_is_file` and `test_path_is_missing`,
> which instead provide more informative error messages.
> 
> Note that `! test -f` checks if a path is not a file, while
> `test_path_is_missing` verifies that a path does not exist. In this specific
> case the tests are meant to check the absence of the path, making
> `test_path_is_missing` a valid replacement.