Use 'set __COMPAT_LAYER=' in Windows CI builds.

It is suggested at
https://github.com/commercialhaskell/stack/issues/3765
that this may solve the "access violation" we're currently
getting on Windows CI with ghc 8.8.

.github/workflows/ci.yml

@@ -119,13 +119,19 @@ jobs:
     #     key:          ${{ runner.os }}-stack-work-${{ hashFiles('stack.yaml') }}
     #     restore-keys: ${{ runner.os }}-stack-work
 
+    # Note: the set __COMPAT_LAYER= is needed to avoid an access
+    # violation error; see
+    # https://github.com/commercialhaskell/stack/issues/3765
+
     - name: Install dependencies
       run: |
+          set __COMPAT_LAYER=
           stack update
           stack test --dependencies-only --fast
     - name: Build and test
       shell: cmd
       run: |
+          set __COMPAT_LAYER=
           stack test --fast --test-arguments=--hide-successes
 
   macos:

.github/workflows/nightly.yml

@@ -48,6 +48,7 @@ jobs:
           choco install haskell-stack
     - name: Install dependencies
       run: |
+          set __COMPAT_LAYER=
           stack update
           stack build --dependencies-only pandoc pandoc-citeproc
     - name: Build artifacts
@@ -56,6 +57,7 @@ jobs:
           for /f %%a in ('powershell -Command "Get-Date -format yyyy-MM-dd"') do set THEDATE=%%a
           set ARTIFACTS=%CD%\nightly-windows\pandoc-nightly-windows-%THEDATE%
           mkdir %ARTIFACTS%
+          set __COMPAT_LAYER=
           stack build pandoc pandoc-citeproc
           forfiles /P .\.stack-work\install /M pandoc*.exe /S /C "cmd /C copy @path %%ARTIFACTS%%"
           copy COPYRIGHT %ARTIFACTS%