Update src/content/docs/cache/how-to/cache-keys.mdx

Co-authored-by: marciocloudflare <[email protected]>

Author: angelampcosta

src/content/docs/cache/how-to/cache-keys.mdx

@@ -61,7 +61,7 @@ Be aware that changes in the SSL setting can lead to cache invalidation when usi
 
 - Moving from **Flexible** to **Full**, **Full (strict)**, or **Strict** similarly changes the origin scheme to HTTPS and causes a cache bust.
 
-Understanding how $scheme interacts with your caching configuration is essential when modifying SSL modes to avoid unexpected cache behavior.
+Understanding how `$scheme` interacts with your caching configuration is essential when modifying SSL modes to avoid unexpected cache behavior.
 
 ### Cache Level: Ignore Query String