Fix docs publishing (#203)

* try and fix the docs publishing

* only do it on main now

Author: nplasterer

.github/workflows/docs.yml

@@ -10,7 +10,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
+      - name: Setup Java
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'adopt'
+          java-version: '17'
       - name: Build documentation
         run: ./gradlew dokkaHtml
       - name: Publish documentation