Test build on GHC 9.0.1

Author: adithyaov

.github/workflows/packcheck.yml

@@ -98,7 +98,8 @@ jobs:
         name: [ci]
         # Uncomment GHC versions you want the CI to run on.
         ghc_version:
-          [ 8.10.3
+          [ 9.0.1
+          , 8.10.3
           , 8.8.4
           , 8.6.5
           , 8.4.4

unicode-transforms.cabal

@@ -21,6 +21,7 @@ tested-with:    GHC==7.10.3
               , GHC==8.6.5
               , GHC==8.8.4
               , GHC==8.10.3
+              , GHC==9.0.1
 build-type:     Simple
 extra-source-files:
     Changelog.md