Bug 1483080 [wpt PR 12450] - Ensure templated tests do set a Content-Type: text/html HTTP header, a=testonly

Automatic update from web-platform-testsEnsure templated tests do set a Content-Type: text/html HTTP header (#12450)

--

wpt-commits: 36c74ce6b47fb657411cd8dae7d2c9c8f722af66
wpt-pr: 12450

testing/web-platform/meta/MANIFEST.json

@@ -637675,7 +637675,7 @@
    "support"
   ],
   "tools/serve/serve.py": [
-   "60636d8b7a9f4d8eb0f16316cf208affc88103f2",
+   "6e977066af701a4c5dfc173187110b0e01a03e7e",
    "support"
   ],
   "tools/serve/test_serve.py": [

testing/web-platform/tests/tools/serve/serve.py

@@ -155,6 +155,7 @@ class WrapperHandler(object):
 
 class HtmlWrapperHandler(WrapperHandler):
     global_type = None
+    headers = [('Content-Type', 'text/html')]
 
     def check_exposure(self, request):
         if self.global_type: