Fix GitHub Actions by installing groff on Mac

.github/workflows/ci.yml

@@ -4,6 +4,7 @@ on:
   push:
     branches:
       - main
+      - fix-ci
 
   pull_request:
     branches:
@@ -31,6 +32,8 @@ jobs:
       run: brew install openssl && brew info openssl
     - name: Install XQuartz
       run: brew install xquartz --cask && brew info xquartz
+    - name: Install groff
+      run: brew install groff && brew info groff
     - name: Compile
       run: make -C GUI/xephem
     - name: Test