KNOWN_BUGS: remove "HTTP/3 multipart POST with quiche fails"

It works now

docs/KNOWN_BUGS

@@ -159,7 +159,6 @@ problems may have been fixed or changed somewhat since this was written.
  18. HTTP/3
  18.1 If the HTTP/3 server closes connection during upload curl hangs
  18.2 Uploading HTTP/3 files gets interrupted at certain file sizes
- 18.6 HTTP/3 multipart POST with quiche fails
  18.8 HTTP/3 does not support client certs
  18.9 connection migration does not work
 
@@ -1125,10 +1124,6 @@ problems may have been fixed or changed somewhat since this was written.
 
  See https://github.com/curl/curl/issues/6510
 
-18.6 HTTP/3 multipart POST with quiche fails
-
- https://github.com/curl/curl/issues/7125
-
 18.8 HTTP/3 does not support client certs
 
  aka "mutual authentication".