Add new package doctest-parallel. Allow haddock failure (due to commercialhaskell#5014)

Author: lehins

build-constraints.yaml

@@ -2190,6 +2190,7 @@ packages:
 
     "Martijn Bastiaan <[email protected]> @martijnbastiaan":
         - aeson-pretty
+        - doctest-parallel
 
     "Athan Clark <[email protected]> @athanclark":
         - aeson-attoparsec
@@ -7649,6 +7650,7 @@ expected-haddock-failures:
     - hw-ip # https://github.com/commercialhaskell/stackage/issues/5014
     - hw-json # https://github.com/commercialhaskell/stackage/issues/5014
     - hw-rankselect
+    - doctest-parallel # https://github.com/commercialhaskell/stackage/issues/5014
 
 # end of expected-haddock-failures