Work around for dubious ownership git error

    fatal: detected dubious ownership in repository at '/__w/dd-trace-rb/dd-trace-rb'
    To add an exception for this directory, call:

    	git config --global --add safe.directory /__w/dd-trace-rb/dd-trace-rb

This creeps up e.g when container user info doesn't match host info (e.g
via a host volume mount).

spec/datadog/release_gem_spec.rb

@@ -62,7 +62,7 @@
 
         expect(gemspec.files)
           .to match_array(
-            `git ls-files -z`
+            `git -c safe.directory='*' ls-files -z`
               .split("\x0")
               .reject { |f| f.match(directories_excluded) }
               .reject { |f| f.match(single_files_excluded) }