Wrap 2 more BASE_URL usages with str()

In 59372aba33 a lazily evaluated BASE_URL tool was introduced.
I found 2 more cases in which BASE_URL was not "collapsed into a
string" magically by `__add__`, one of which actually causing
an `Object of type TenantBaseURL is not JSON serializable`

bugsink/debug_views.py

@@ -203,7 +203,7 @@ def csrf_debug(request):
         # We do this here, and not in urls.py, because urls.py cannot be changed on-demand in tests
         raise Http404("This view is only available in DEBUG_CSRF mode.")
 
-    context = {"relevant_settings": {"BASE_URL": get_settings().BASE_URL}}
+    context = {"relevant_settings": {"BASE_URL": str(get_settings().BASE_URL)}}
     context["relevant_settings"].update({k: getattr(settings, k) for k in [
         "ALLOWED_HOSTS",
         "SECURE_PROXY_SSL_HEADER",

ingest/models.py

@@ -48,7 +48,7 @@ class StoreEnvelope:
 
         # arguably "debug", but if you turned StoreEnvelope on, you probably want to use its results "soon", and I'd
         # rather not have another thing for people to configure.
-        logger.info("envelope stored, available at %s%s", get_settings().BASE_URL, envelope.get_absolute_url())
+        logger.info("envelope stored, available at %s%s", str(get_settings().BASE_URL), envelope.get_absolute_url())
 
 
 class DontStoreEnvelope:

phonehome/tasks.py

@@ -75,7 +75,7 @@ def _make_message_body():
 
         "settings": {
             # Settings that tell us "who you are", and are relevant in the context of licensing.
-            "BASE_URL": get_settings().BASE_URL,
+            "BASE_URL": str(get_settings().BASE_URL),
             "SITE_TITLE": get_settings().SITE_TITLE,
             "DEFAULT_FROM_EMAIL": settings.DEFAULT_FROM_EMAIL,