first cut at API checking

The API files are empty in this commit, and will hopefully be
filled in in later (to be squashed or amended) commits.

.github/workflows/check-api.yml

@@ -58,7 +58,7 @@ jobs:
       # isn't enough cache space to make a third cache, even though this is a very limited build.
       - name: Build Cabal with environment files
         shell: bash
-        run: cabal build Cabal-syntax Cabal --write-environment-files=always --project-file=cabal.release.project
+        run: cabal build Cabal-syntax Cabal --write-ghc-environment-files=always --project-file=cabal.release.project
 
       - name: Check Cabal-syntax and Cabal APIs
         run: |