Bug 1684953 [wpt PR 27037] - Port format_json.py to Python 3, a=testonly

Automatic update from web-platform-tests
Port format_json.py to Python 3 (#27037)

This fixes a WPT lint error with Python 3
--

wpt-commits: e0ad10ba0000c8c8a0c8a7c36256694eaf4563d4
wpt-pr: 27037

testing/web-platform/tests/import-maps/data-driven/tools/format_json.py

@@ -12,7 +12,7 @@ $ python tools/format_json.py resources/*.json
 
 def main():
     for filename in sys.argv[1:]:
-        print filename
+        print(filename)
         try:
             spec = json.load(
                 open(filename, u'r'), object_pairs_hook=collections.OrderedDict)