Take sydtest's typed scenario paths
sydtest's `scenarioDir` now hands the callback a `Path Rel File` rather than a
`FilePath` (NorfairKing/sydtest "Let a scenario carry whether it is a file or a
directory"). This repo has one scenario, and it wants a string in every use it
has, so it names it once:
```haskell
scenarioDir [reldir|test_resources|] $ \file ->
let fp = fromRelFile file
in when (".html" `isSuffixOf` fp) $ do
...
```
The suffix test stays a suffix test rather than becoming `fileExtension`: the
two disagree about a file called exactly `.html`, and nothing here needs that
argued about.
`path` joins the test suite's dependencies for `reldir` and `fromRelFile`.
### Why now
nix-ci builds this package from source with its own sydtest, so bumping sydtest
there breaks this test suite. This repo has no sydtest input of its own to bump,
so it is compatible with whichever sydtest the consuming flake supplies — which
means this change requires the new one.
Verified by building it inside nix-ci with sydtest at master.