test: make parse-hwdb compatible with older pyparsing versions

Follow-up to e77fed207a.

hwdb.d/parse_hwdb.py

@@ -33,11 +33,22 @@ try:
                            OneOrMore, Combine, Or, Optional, Suppress, Group,
                            nums, alphanums, printables,
                            stringEnd, pythonStyleComment,
-                           ParseBaseException, __diag__)
+                           ParseBaseException)
 except ImportError:
     print('pyparsing is not available')
     sys.exit(77)
 
+try:
+    from pyparsing import __diag__
+
+    __diag__.warn_multiple_tokens_in_named_alternation = True
+    __diag__.warn_ungrouped_named_tokens_in_collection = True
+    __diag__.warn_name_set_on_empty_Forward = True
+    __diag__.warn_on_multiple_string_args_to_oneof = True
+    __diag__.enable_debug_on_named_expressions = True
+except ImportError:
+    pass
+
 try:
     from evdev.ecodes import ecodes
 except ImportError:
@@ -50,12 +61,6 @@ except ImportError:
     # don't do caching on old python
     lru_cache = lambda: (lambda f: f)
 
-__diag__.warn_multiple_tokens_in_named_alternation = True
-__diag__.warn_ungrouped_named_tokens_in_collection = True
-__diag__.warn_name_set_on_empty_Forward = True
-__diag__.warn_on_multiple_string_args_to_oneof = True
-__diag__.enable_debug_on_named_expressions = True
-
 EOL = LineEnd().suppress()
 EMPTYLINE = LineEnd()
 COMMENTLINE = pythonStyleComment + EOL