Update "Custom Ports" known issue to reflect dev-time only behaviour

The change made in PR cloudflare#7514 assumes that custom ports work with HTTP requests, however, this is not true.

PR cloudflare#5255 did correctly mention the dev-time discrepancy but it was not merged.

Author: xdjoshuaaz

content/workers/platform/known-issues.md

@@ -45,7 +45,9 @@ return await fetch(request);
 
 ## Custom ports
 
-For Workers subrequests, custom ports are ignored when using HTTPS and are instead always sent to port `443`. When using HTTP, custom ports are respected.
+For Workers subrequests, custom ports are ignored and requests are sent to the scheme's default port, such as `443` for HTTPS.
+
+This behaviour is not present in local development or when using Quick Edit in the dashboard.
 
 For example:
 
@@ -57,4 +59,4 @@ is the equivalent of:
 
 ```js
 await fetch('https://example.com/foo')
-```
+```