Do not lint .h files in regression/

Author: tautschnig

scripts/cpplint.py

@@ -6506,7 +6506,7 @@ def ProcessFile(filename, vlevel, extra_check_functions=[]):
   if Search(r'_builtin_headers(_[a-z0-9_-]+)?\.h$', filename):
     return
 
-  if Search(r'regression/.*\.cpp', filename):
+  if Search(r'regression/.*\.(cpp|h)', filename):
     return
 
   if not ProcessConfigOverrides(filename):