Rename multi-OS CI to "MacOS, Ubuntu, Windows"; restrict to last 3 GHCs

Author: andreasabel

.github/workflows/haskell.yml

@@ -1,5 +1,4 @@
-name: Haskell CI
-
+name: MacOS, Ubuntu, Windows
 
 on: [push, pull_request]
 
@@ -10,7 +9,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ghc: ['9.2.1', '9.0.2', '8.10.7', '8.8.4', '8.6.5']
+        ghc: ['9.2.1', '9.0.2', '8.10.7']
         os: [ubuntu-latest, macOS-latest, windows-latest]
     steps:
     - uses: actions/checkout@v2