`Potential security risk` warning in the web browser (domain mismatch in the the TLS certificate)

[opk12]

$ openssl s_client -connect missingmaps.org:443 2>/dev/null  | head
CONNECTED(00000003)
---
Certificate chain
 0 s:C = US, ST = California, L = San Francisco, O = "GitHub, Inc.", CN = *.github.com
   i:C = US, O = DigiCert Inc, CN = DigiCert TLS RSA SHA256 2020 CA1
 1 s:C = US, O = DigiCert Inc, CN = DigiCert TLS RSA SHA256 2020 CA1
   i:C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert Global Root CA
---
Server certificate
-----BEGIN CERTIFICATE-----