CI: test with GHC 9.0.1

.github/workflows/ci.yml

@@ -68,11 +68,16 @@ jobs:
             prefix: ''
             cabalopts: ''
             testopts: '--test-option=--hide-successes'
-          - ghc: '8.10.2'
+          - ghc: '8.10.4'
             cabal: '3.2'
             prefix: ''
             cabalopts: '-ftrypandoc'
             testopts: '--test-option=--hide-successes'
+          - ghc: '9.0.1'
+            cabal: '3.4'
+            prefix: ''
+            cabalopts: ''
+            testopts: '--test-option=--hide-successes'
     steps:
     - uses: actions/checkout@v2
 

pandoc.cabal

@@ -12,7 +12,7 @@ stability:       alpha
 homepage:        https://pandoc.org
 category:        Text
 tested-with:     GHC == 8.2.2, GHC == 8.4.4, GHC == 8.6.5,
-                 GHC == 8.8.4, GHC == 8.10.2
+                 GHC == 8.8.4, GHC == 8.10.2, GHC == 9.0.1
 synopsis:        Conversion between markup formats
 description:     Pandoc is a Haskell library for converting from one markup
                  format to another, and a command-line tool that uses