Fix the docs build when CI is triggered by a tag (#1662)

Co-authored-by: Ralf W. Grosse-Kunstleve <rwgkio@gmail.com>

Author: mdboom

.github/workflows/ci.yml

@@ -221,6 +221,7 @@ jobs:
     uses: ./.github/workflows/build-docs.yml
     with:
       build-ctk-ver: ${{ needs.ci-vars.outputs.CUDA_BUILD_VER }}
+      is-release: ${{ github.ref_type == 'tag' }}
 
   checks:
     name: Check job status