Merge onto solution branch automatically

.github/workflows/ci.yml

@@ -103,10 +103,14 @@ jobs:
       - name: Cabal build dependencies
         run: cabal build all --enable-tests --only-dependencies
 
-      - name: Check whether solution branch only contains diffs in the Koans
+      - name: Check whether solution branch only contains diffs in the Koans, and merge
         run: |
+          git fetch origin main
           git fetch origin solution
+          git checkout solution
+          git merge origin/main
           git diff origin/solution --exit-code  -- ':(exclude)koans/**/Koan.hs'
+          git push
 
       - name: Check out solution branch
         uses: actions/checkout@v4