keyring: add 890C08DB8579162FEE0DF9DB8BEAB4DFCF555EF4 to keyring

[BethGriggs]

./cli.sh add 890C08DB8579162FEE0DF9DB8BEAB4DFCF555EF4

Refs: #21

---

@RafaelGSS's key was added by #16 but not added to the keychain. This PR adds it to the keyring via the CLI:

$ ./cli.sh add 890C08DB8579162FEE0DF9DB8BEAB4DFCF555EF4

After adding, I can verify the v19.4.0 signatures using the keyring:

$ GNUPGHOME=~/release-keys/gpg gpg --verify SHASUMS256.txt.sig SHASUMS256.txt  
gpg: Signature made Fri  6 Jan 13:15:00 2023 GMT
gpg:                using RSA key 890C08DB8579162FEE0DF9DB8BEAB4DFCF555EF4
gpg: Good signature from "RafaelGSS <rafael.nunu@hotmail.com>" [unknown]
...

[RafaelGSS]

Thank you!