Don't let julia-actions delete cache

Author: penelopeysm

.github/workflows/preview.yml

@@ -10,7 +10,6 @@ concurrency:
   group: docs
 
 permissions:
-  actions: write
   contents: write
   pull-requests: write
 
@@ -31,6 +30,8 @@ jobs:
 
       - name: Load Julia packages from cache
         uses: julia-actions/cache@v2
+        with:
+          delete-old-caches: false
 
       # Note: needs resolve() to fix #518
       - name: Instantiate Julia environment