Set documenter key

Author: darnstrom

.github/workflows/documentation.yml

@@ -25,4 +25,5 @@ jobs:
       - name: Build and deploy
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          DOCUMENTER_KEY: ${{ secrets.DOCUMENTER_KEY }}
         run: julia --project=docs/ docs/make.jl