Latest CI workflow also ran into this linkcheck failure

1. Attempt 1 failed
2. Attempt 2 failed
3. Attempt 3 succeeded

I saw this several times last week but forgot to report. +1 for ignoring.

This error

Failed to establish a new connection: [Errno 101] Network is unreachable

is ultimately not the fault of the remote host (i.e. gnu.org), but a configuration issue on the local host (i.e. GitHub Actions runner).

I'm guessing that something in linkcheck is resolving the IPv6 address of gnu.org (2001:470:142:5::116) instead of the IPv4 address, but the IPv6 address is unroutable from the GitHub Actions runner.

For example, a host with working IPv6 vs. one without:

$ ping 2001:470:142:5::116
PING 2001:470:142:5::116(2001:470:142:5::116) 56 data bytes
64 bytes from 2001:470:142:5::116: icmp_seq=1 ttl=55 time=12.8 ms
64 bytes from 2001:470:142:5::116: icmp_seq=2 ttl=55 time=12.8 ms
^C
--- 2001:470:142:5::116 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1002ms
rtt min/avg/max/mdev = 12.835/12.839/12.844/0.004 ms

$ ping 2001:470:142:5::116
ping: connect: Network is unreachable

Ignoring this particular link is fine for now, but if we find ourselves repeatedly hitting ENETUNREACH or similar errors that have nothing to do with the remote host itself, we should step back and address the root of the errors.