Update PKI CA test

Previously if a client tries to connect to a server but it does
not have the CA signing cert installed and trusted it will get
an UNTRUSTED_ISSUER error from NSS. In the latest NSS the error
has changed to UNKNOWN_ISSUER, so the test has been updated
accordingly.

.github/workflows/pki-ca-test.yml

@@ -142,7 +142,7 @@ jobs:
 
  # check stderr
  cat > expected << EOF
- WARNING: UNTRUSTED ISSUER encountered on 'CN=pki.example.com,OU=pki-tomcat,O=EXAMPLE' indicates a non-trusted CA cert 'CN=CA Signing Certificate,OU=pki-tomcat,O=EXAMPLE'
+ WARNING: UNKNOWN_ISSUER encountered on 'CN=pki.example.com,OU=pki-tomcat,O=EXAMPLE' indicates an unknown CA cert 'CN=CA Signing Certificate,OU=pki-tomcat,O=EXAMPLE'
  Trust this certificate (y/N)? SEVERE: FATAL: SSL alert sent: BAD_CERTIFICATE
  IOException: Unable to write to socket: Failed to write to socket: (-5987) Invalid function argument.
  EOF
@@ -169,8 +169,8 @@ jobs:
 
  # check stderr
  cat > expected << EOF
+ WARNING: UNKNOWN_ISSUER encountered on 'CN=pki.example.com,OU=pki-tomcat,O=EXAMPLE' indicates an unknown CA cert 'CN=CA Signing Certificate,OU=pki-tomcat,O=EXAMPLE'
  WARNING: BAD_CERT_DOMAIN encountered on 'CN=pki.example.com,OU=pki-tomcat,O=EXAMPLE' indicates a common-name mismatch
- WARNING: UNTRUSTED ISSUER encountered on 'CN=pki.example.com,OU=pki-tomcat,O=EXAMPLE' indicates a non-trusted CA cert 'CN=CA Signing Certificate,OU=pki-tomcat,O=EXAMPLE'
  Trust this certificate (y/N)? SEVERE: FATAL: SSL alert sent: BAD_CERTIFICATE
  IOException: Unable to write to socket: Failed to write to socket: (-12276) Unable to communicate securely with peer: requested domain name does not match the server's certificate.
  EOF
@@ -194,7 +194,7 @@ jobs:
 
  # check stderr
  cat > expected << EOF
- WARNING: UNTRUSTED ISSUER encountered on 'CN=pki.example.com,OU=pki-tomcat,O=EXAMPLE' indicates a non-trusted CA cert 'CN=CA Signing Certificate,OU=pki-tomcat,O=EXAMPLE'
+ WARNING: UNKNOWN_ISSUER encountered on 'CN=pki.example.com,OU=pki-tomcat,O=EXAMPLE' indicates an unknown CA cert 'CN=CA Signing Certificate,OU=pki-tomcat,O=EXAMPLE'
  Trust this certificate (y/N)?
  EOF