Bug 1686421 - Enable network.dns.upgrade_with_https_rr only on nightly, r=dragana

Differential Revision: https://phabricator.services.mozilla.com/D101597

modules/libpref/init/StaticPrefList.yaml

@@ -8850,7 +8850,7 @@
 # available.
 - name: network.dns.upgrade_with_https_rr
   type: RelaxedAtomicBool
-  value: @IS_EARLY_BETA_OR_EARLIER@
+  value: @IS_NIGHTLY_BUILD@
   mirror: always
 
 # Whether to use HTTPS RR as AltSvc