fix: skip test unless it implements gat

Co-authored-by: Francis Bogsanyi <[email protected]>

Author: robertlaurin

instrumentation/dalli/test/opentelemetry/instrumentation/dalli/instrumentation_test.rb

@@ -129,6 +129,8 @@
     end
 
     it 'supports gat' do
+      skip unless dalli.respond_to?(:gat)
+
       dalli.gat('foo')
 
       _(exporter.finished_spans.size).must_equal 1