fix(active-job): Handle missing CLOCK_THREAD_CPUTIME_ID on JRuby

Use defined? guard instead of begin/rescue since JRuby raises
NameError (constant doesn't exist) rather than Errno::EINVAL.

Author: bdewater-thatch

instrumentation/active_job/lib/opentelemetry/instrumentation/active_job/handlers/perform.rb

@@ -118,12 +118,11 @@ def now_gc
             end
           end
 
-          begin
-            Process.clock_gettime(Process::CLOCK_THREAD_CPUTIME_ID, :float_millisecond)
+          if defined?(Process::CLOCK_THREAD_CPUTIME_ID)
             def now_cpu
               Process.clock_gettime(Process::CLOCK_THREAD_CPUTIME_ID, :float_millisecond)
             end
-          rescue Errno::EINVAL
+          else
             def now_cpu
               0.0
             end