Fix scanner comparison error

If one of the key arguments is nil, comparison breaks and fails
report parsing

Issue https://gitlab.com/gitlab-org/gitlab/-/issues/332719

Changelog: fixed

lib/gitlab/ci/reports/security/scanner.rb

@@ -39,7 +39,7 @@ module Gitlab
           end
 
           def <=>(other)
-            sort_keys <=> other.sort_keys
+            sort_keys.compact <=> other.sort_keys.compact
           end
 
           protected

spec/lib/gitlab/ci/reports/security/scanner_spec.rb

@@ -110,6 +110,7 @@ RSpec.describe Gitlab::Ci::Reports::Security::Scanner do
         { external_id: 'gemnasium-python', name: 'foo', vendor: 'bar' } | { external_id: 'bandit', name: 'foo', vendor: 'bar' }           | 1
         { external_id: 'bandit', name: 'foo', vendor: 'bar' }           | { external_id: 'semgrep', name: 'foo', vendor: 'bar' }          | -1
         { external_id: 'semgrep', name: 'foo', vendor: 'bar' }          | { external_id: 'unknown', name: 'foo', vendor: 'bar' }          | -1
+        { external_id: 'gemnasium', name: 'foo', vendor: 'bar' }        | { external_id: 'gemnasium', name: 'foo', vendor: nil }          | 1
       end
 
       with_them do