httppeer: make a message translatable

This message has been overlooked by check-code, because it starts with
non-alphabet character ('(').

Making this message translatable seems reasonable, because exception
message below in same function is already translatable

  - 'cannot create new http repository'

This is also a part of preparation for making "missing _() in ui
message" detection of check-code more exact.

mercurial/httppeer.py

@@ -302,7 +302,7 b' def instance(ui, path, create):'
     except error.RepoError as httpexception:
         try:
             r = statichttprepo.instance(ui, "static-" + path, create)
-            ui.note('(falling back to static-http)\n')
+            ui.note(_('(falling back to static-http)\n'))
             return r
         except error.RepoError:
             raise httpexception # use the original http RepoError instead