Also test with GHC 8.6.5

.github/workflows/ci.yaml

@@ -18,6 +18,10 @@ jobs:
           - 8.8.4
         cabal:
           - 3.2.0.0
+        include:
+          - os: ubuntu-18.04
+            ghc: 8.6.5
+            cabal: 3.2.0.0
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2
@@ -37,7 +41,7 @@ jobs:
             ${{ matrix.os }}-${{ matrix.ghc }}-
       - run: cabal test --test-show-details direct
       - run: cabal sdist
-      - if: matrix.os == 'ubuntu-18.04'
+      - if: matrix.os == 'ubuntu-18.04' && matrix.ghc == '8.8.4'
         uses: actions/upload-artifact@v2
         with:
           path: dist-newstyle/sdist/brittany-*.tar.gz