Update tests/test-values.yaml with Digicert CA Cert

Summary

While testing a Kiali renovate update I ran into TLS errors when trying to authenticating with a local keycloak

[x509: certificate signed by unknown authority]
(https://keycloak.dev.bigbang.mil/auth/realms/baby-yoda/.well-known/openid-configuration": 
tls: failed to verify certificate: x509: certificate signed by unknown authority)

The TLS certs were recently updated. Along with the update the issuer changed from Letsencrypt to Digicert.

Resolution:

The tests/test-values.yaml will need to be updated with the DigiCert CA cert.