Use --allow-newer when testing on 'latest' ghc

Author: koalaman

.github/workflows/build.yml

@@ -49,6 +49,9 @@ jobs:
     strategy:
       matrix:
         ghc: ['8.0', '8.10', '9.0.1', 'latest']
+        include:
+          - ghc: 'latest'
+            cabal_flags: '--allow-newer'
       # If one version fails, we still want the status of the others
       fail-fast: false
     steps:
@@ -71,7 +74,7 @@ jobs:
       - name: Build and run tests
         run: |
           cd source
-          cabal test
+          cabal test ${{ matrix.cabal_flags }}
 
   build_source:
     name: Build