Run free-disk-space action in security-docs (#639)

Author: reakaleek

.github/workflows/preview-build.yml

@@ -65,7 +65,7 @@ jobs:
           ref: ${{ github.event.pull_request.head.sha || github.ref }}
 
       - name: Free Disk Space
-        if: github.repository == 'elastic/asciidocalypse'
+        if: contains(fromJSON('["elastic/asciidocalypse", "elastic/security-docs"]'), github.repository)
         uses: jlumbroso/free-disk-space@54081f138730dfa15788a46383842cd2f914a1be # v1.3.1
         with:
           tool-cache: false