Update alias count to be new 1000 limit

Author: WalshyDev

src/content/docs/workers/configuration/previews.mdx

@@ -86,7 +86,7 @@ The resulting alias would be associated with this version, and immediately avail
 - Aliases must use only lowercase letters, numbers, and dashes.
 - Aliases must begin with a lowercase letter.
 - The alias and Worker name combined (with a dash) must not exceed 63 characters due to DNS label limits.
-- Only the 20 most recently used aliases are retained. When a new alias is created beyond this limit, the least recently used alias is deleted.
+- Only the 1000 most recently deployed aliases are retained. When a new alias is created beyond this limit, the least recently deployed alias is deleted.
 
 ## Manage access to Preview URLs