Properly parse time in alert payload

https://gitlab.com/gitlab-org/gitlab/-/issues/321304

Properly parse time passed as time in seconds in alert payload

Changelog: fixed

lib/gitlab/alert_management/payload/base.rb

@@ -193,7 +193,7 @@ module Gitlab
 
         def parse_time(value)
           Time.parse(value).utc
-        rescue ArgumentError
+        rescue ArgumentError, TypeError
         end
 
         def parse_integer(value)

spec/lib/gitlab/alert_management/payload/base_spec.rb

@@ -89,6 +89,12 @@ RSpec.describe Gitlab::AlertManagement::Payload::Base do
 
         it { is_expected.to be_nil }
       end
+
+      context 'with time in seconds' do
+        let(:raw_payload) { { 'test' => 1618877936 } }
+
+        it { is_expected.to be_nil }
+      end
     end
 
     context 'with an integer type provided' do