It seems that fetchmail doesn't enable SNI for it's TLS connection
Try adding `--sslproto TLS1' to fetchmail's arguments.
I guess the core issue is that for Google servers when using TLS 1.2 SNI
isn't required, but for TLS 1.3 it is; well, let me rephrase that. If
you negotiate TLS 1.3 you get the bogus certificate if you don't send a
SNI. But it seems like the 'right' solution is we should be sending a
SNI to avoid this problem?