docs: Fix PR number in release notes - rename to 6711

Updates the release notes file name and PR reference from 6708 to 6711.

Author: PastaPastaPasta

doc/release-notes-6708.md renamed to doc/release-notes-6711.md

@@ -3,4 +3,4 @@ Updated settings
 
 - BIP157 compact block filters are now enabled by default. This improves privacy for light clients
   and enables better support for pruned nodes. The `-blockfilterindex` option now defaults to `basic`
-  instead of `0` (disabled), and the `-peerblockfilters` option now defaults to `true` instead of `false` (#6708).
+  instead of `0` (disabled), and the `-peerblockfilters` option now defaults to `true` instead of `false` (#6711).