Fix doc build

Author: blegat

.github/workflows/documentation.yml

@@ -14,6 +14,8 @@ jobs:
         with:
           # Build documentation on latest release
           version: '1'
+      - name: Install dependencies
+        run: julia --project=docs/ -e 'using Pkg; Pkg.develop(PackageSpec(path=pwd())); Pkg.instantiate()'
       - name: Build and deploy
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} # For authentication with GitHub Actions token