Fixes CI branch condition syntax in GitHub Actions

Author: AndrewSazonov

.github/workflows/build-docs.yml

@@ -177,7 +177,7 @@ jobs:
     runs-on: ubuntu-latest
 
     # Triggered on push to develop or master branch only
-    if: env.CI_BRANCH == 'develop' || env.CI_BRANCH == 'master'
+    if: ${{ env.CI_BRANCH == 'develop' || env.CI_BRANCH == 'master' }}
 
     steps:
       # Deploy the static files created in the previous job to GitHub Pages