Bug 1928291 - Enable sending Referer header from Refresh by default. r=smaug,peterv,dom-core

Intent to ship:

https://groups.google.com/a/mozilla.org/g/dev-platform/c/E_fGBCm0NrQ

Differential Revision: https://phabricator.services.mozilla.com/D231364

modules/libpref/init/StaticPrefList.yaml

@@ -12834,7 +12834,7 @@
   # in response to a Refresh header.
 - name: network.http.referer.sendFromRefresh
   type: bool
-  value: @IS_NIGHTLY_BUILD@
+  value: true
   mirror: always
 
 # false=real referer, true=spoof referer (use target URI as referer).