Make ContextPayloadProcessor spec more robust

This spec intends to test that we deep merge information from the
application context into the Sentry event. It appears that prior specs
can leak some application context (or some Sentry context), but we can
make the spec more robust _and_ truer to the intent by using `include`
instead of `eq`.

spec/lib/gitlab/error_tracking/processor/context_payload_processor_spec.rb

@@ -23,10 +23,10 @@ RSpec.describe Gitlab::ErrorTracking::Processor::ContextPayloadProcessor do
     end
 
     it 'merges the context payload into event payload', :aggregate_failures do
-      expect(result_hash[:user]).to eq(ip_address: '127.0.0.1', username: 'root')
+      expect(result_hash[:user]).to include(ip_address: '127.0.0.1', username: 'root')
 
       expect(result_hash[:tags])
-        .to eq(priority: 'high',
+        .to include(priority: 'high',
                locale: 'en',
                program: 'test',
                feature_category: 'feature_a',