(CAT-2026) Update how pdk test unit --list detects an error

A recent change has caused the information returned to be in a slightly different format.

lib/pdk/tests/unit.rb

@@ -246,10 +246,11 @@ def self.list(options = {})
         raise PDK::CLI::FatalError, format('Failed to find valid JSON in output from rspec: %{output}', output: output[:stdout]) unless rspec_json
 
         if rspec_json['examples'].empty?
-          rspec_message = rspec_json['messages'][0]
-          return [] if rspec_message == 'No examples found.'
+          rspec_json['messages'].each do |rspec_message|
+            return [] if rspec_message == 'No examples found.'
+          end
 
-          raise PDK::CLI::FatalError, format('Unable to enumerate examples. rspec reported: %{message}', message: rspec_message)
+          raise PDK::CLI::FatalError, format('Unable to enumerate examples. rspec reported: %{message}', message: rspec_json['messages'])
         else
           examples = []
           rspec_json['examples'].each do |example|