fix: use correct host in URL construction

[miketheman]

From #17324

This catches us often in tasks, defaulting to localhost.

[miketheman]

I did some code spelunking to see if this was relatively easy to make "standard", and here's the path:

• construct a request-like object when called via get_request via pyramid.scripting.prepare(registry=registry)
• as we don't pass a request (how could we? it doesn't exist yet!), only a registry to prepare()
• it in turn calls _make_request with a path of / and registry
• inside webob.request.BaseRequest.blank, where a call to environ_from_url(path='/') will return http://localhost:80/ from this logic
  It doesn't look like there's an opportunity to inject a domain setting from the registry along that path.

I experimented with crafting a dummy request object by pulling the domain from the settings, but since we don't have a full URL handy, it doesn't work well.

diff --git a/warehouse/tasks.py b/warehouse/tasks.py
index 830906cb8..ce0db84a3 100644
--- a/warehouse/tasks.py
+++ b/warehouse/tasks.py
@@ -26,6 +26,7 @@ import transaction
 import venusian

 from kombu import Queue
+from pyramid.request import Request
 from pyramid.threadlocal import get_current_request
 from urllib3.util import parse_url

@@ -92,7 +93,8 @@ class WarehouseTask(celery.Task):
     def get_request(self):
         if not hasattr(self.request, "pyramid_env"):
             registry = self.app.pyramid_config.registry
-            env = pyramid.scripting.prepare(registry=registry)
+            _request = Request.blank("/", base_url=registry.settings.get("warehouse.domain"))
+            env = pyramid.scripting.prepare(request=_request, registry=registry)
             env["request"].tm = transaction.TransactionManager(explicit=True)
             env["request"].timings = {"new_request_start": time.time() * 1000}
             env["request"].remote_addr = "127.0.0.1"

with a WAREHOUSE_DOMAIN of pypi.org ends up as:

'request': <Request at 0xffff8bad6480 GET http://localhostpypi.org/>`

Going to proceed with these changes for now.