Fix missing environment variable for tests

.github/workflows/build_docs.yml

@@ -70,6 +70,8 @@ jobs:
   test:
     runs-on: ubuntu-latest
     needs: [hexdoc]
+    env:
+      GITHUB_PAGES_URL: ${{ needs.hexdoc.outputs.pages-url }}
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4

.github/workflows/hexdoc.yml

@@ -31,6 +31,9 @@ on:
       publish-release:
         description: Value of publish-release input for convenience.
         value: ${{ inputs.publish-release }}
+      pages-url:
+        description: Current GitHub Pages url for this repo.
+        value: ${{ jobs.build.outputs.pages-url }}
 
 permissions:
   contents: read