test(spec): inline config into test suite

Previously, information about each test-suite was repeated in 3 separate
places:
- as a label and as implicit knowledge in the test-suite itself,
- as a comment in Main.hs, and
- as a configuration in SpecHelper.hs.

With this change, there will be a single source of truth in the test
suite itself. This will allow a single test-suite to easily test
multiple different configurations.

test/spec/Feature/ConcurrentSpec.hs

@@ -5,7 +5,6 @@
 module Feature.ConcurrentSpec where
 
 import Control.Concurrent.Async (mapConcurrently)
-import Network.Wai              (Application)
 
 import Control.Monad.Base
 import Control.Monad.Trans.Control
@@ -16,10 +15,11 @@ import Test.Hspec.Wai
 import Test.Hspec.Wai.Internal
 import Test.Hspec.Wai.JSON
 
-import Protolude hiding (get)
+import Protolude  hiding (get)
+import SpecHelper
 
-spec :: SpecWith ((), Application)
-spec =
+spec :: SpecWithConfig
+spec withConfig = withConfig baseCfg $
   describe "Querying in parallel" $
     it "should not raise 'transaction in progress' error" $
       raceTest 10 $