Fix missing request_id on event

lib/datadog/tracing/contrib/stripe/request.rb

@@ -47,8 +47,9 @@ def tag_span(span, event)
 
             # Measure service stats
             Contrib::Analytics.set_measured(span)
-
-            span.set_tag(Ext::TAG_REQUEST_ID, event.request_id)
+            # `5.38.0` Add request_id to RequestEndEvent
+            # https://github.com/stripe/stripe-ruby/blob/master/CHANGELOG.md#5380---2021-08-10
+            span.set_tag(Ext::TAG_REQUEST_ID, event.request_id) if event.respond_to?(:request_id)
             span.set_tag(Ext::TAG_REQUEST_HTTP_STATUS, event.http_status.to_s)
             span.set_tag(Ext::TAG_REQUEST_METHOD, event.method)
             span.set_tag(Ext::TAG_REQUEST_PATH, event.path)

spec/datadog/tracing/contrib/stripe/request_spec.rb

@@ -41,7 +41,9 @@
     expect(spans).to have(1).items
     expect(span.name).to eq('stripe.request')
     expect(span.resource).to eq('stripe.request')
-    expect(span.get_tag('stripe.request.id')).to eq('abc-123-def-456')
+    if Gem::Version.new(Stripe::VERSION) >= Gem::Version.new('5.38.0')
+      expect(span.get_tag('stripe.request.id')).to eq('abc-123-def-456')
+    end
     expect(span.get_tag('stripe.request.http_status')).to eq('200')
     expect(span.get_tag('stripe.request.method')).to eq('get')
     expect(span.get_tag('stripe.request.path')).to eq('/v1/customers/cus_123')
@@ -69,7 +71,9 @@ def object_name
       expect(spans).to have(1).items
       expect(span.name).to eq('stripe.request')
       expect(span.resource).to eq('stripe.customer')
-      expect(span.get_tag('stripe.request.id')).to eq('abc-123-def-456')
+      if Gem::Version.new(Stripe::VERSION) >= Gem::Version.new('5.38.0')
+        expect(span.get_tag('stripe.request.id')).to eq('abc-123-def-456')
+      end
       expect(span.get_tag('stripe.request.http_status')).to eq('200')
       expect(span.get_tag('stripe.request.method')).to eq('get')
       expect(span.get_tag('stripe.request.path')).to eq('/v1/customers/cus_123')