Add DOCUMENTER_KEY secret

To hopefully get documentation builds on tags to happen properly

Author: graeme-a-stewart

.github/workflows/Documentation.yml

@@ -25,4 +25,5 @@ jobs:
       - name: Build and deploy
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} # If authenticating with GitHub Actions token
+          DOCUMENTER_KEY: ${{ secrets.DOCUMENTER_KEY }} # For authentication with SSH deploy
         run: julia --project=docs/ docs/make.jl