Make C code in one packaging test comply with ISO C (#10359).

Patch by Hallvard B Furuseth.
diff --git a/Lib/packaging/tests/test_command_config.py b/Lib/packaging/tests/test_command_config.py
index 6d780c5..dae75b4 100644
--- a/Lib/packaging/tests/test_command_config.py
+++ b/Lib/packaging/tests/test_command_config.py
@@ -29,10 +29,10 @@
         cmd = config(dist)
 
         # simple pattern searches
-        match = cmd.search_cpp(pattern='xxx', body='// xxx')
+        match = cmd.search_cpp(pattern='xxx', body='/* xxx */')
         self.assertEqual(match, 0)
 
-        match = cmd.search_cpp(pattern='_configtest', body='// xxx')
+        match = cmd.search_cpp(pattern='_configtest', body='/* xxx */')
         self.assertEqual(match, 1)
 
     def test_finalize_options(self):