HTTP3.md: adjust the OpenSSL QUIC install instructions

HTTP3.md: adjust the OpenSSL QUIC install instructions

tried installing with old steps but failed
tried with newly added setps and able to build
```
root@ubuntu:~/curl# ./src/curl -V
/root/curl/src/.libs/curl: /lib/x86_64-linux-gnu/libssl.so.3: version `OPENSSL_3.2.0' not found (required by /root/curl/lib/.libs/libcurl.so.4)
root@ubuntu:~/curl#
```
```
root@ubuntu:~/curl# ./src/curl -V
curl 8.6.1-DEV (x86_64-pc-linux-gnu) libcurl/8.6.1-DEV OpenSSL/3.2.0 zlib/1.2.11 brotli/1.0.9 libpsl/0.21.0 nghttp3/1.1.0 OpenLDAP/2.5.16
Release-Date: [unreleased]
Protocols: dict file ftp ftps gopher gophers http https imap imaps ipfs ipns ldap ldaps mqtt pop3 pop3s rtsp smb smbs smtp smtps telnet tftp
Features: alt-svc AsynchDNS brotli HSTS HTTP3 HTTPS-proxy IPv6 Largefile libz NTLM PSL SSL threadsafe TLS-SRP UnixSockets
root@ubuntu:~/curl#
```

Closes #12896