Set staging server preference in reset callback (uplift to 1.12.x)

[emerick]

Uplift of #6267

[kjozwiak]

Looks like the Skip labels were added too late and all the plaforms ran either way. Going to mention the failures that happened below but won't be restarting as it's Android specific and that passed without any failures/issues.

Other failures (not blocking uplift nor restarting as per the above):

test-browser failed on Linux due to RewardsBrowserTest.ShowACPercentInThePanel failing as per https://ci.brave.com/job/pr-brave-browser-rewards-fix-staging-switch-android-2_1.12.xx/1/execution/node/542/log/.

12:47:23  Stack trace:
12:47:23  #0 0x55ce6a128e69 (/home/ubuntu/jenkins/workspace/pr-brave-browser-rewards-fix-staging-switch-android-2_1.12.xx/src/out/Release/brave_browser_tests+0x5c80e68)
12:47:23  
12:47:23  [615/617] RewardsBrowserTest.ShowACPercentInThePanel (CRASHED)
12:47:36  1 test crashed:
12:47:36      RewardsBrowserTest.ShowACPercentInThePanel (../../brave/components/brave_rewards/browser/test/rewards_browsertest.cc:309)

Looks like Win x64 dropped the spot instance/agent removed as per https://ci.brave.com/job/pr-brave-browser-rewards-fix-staging-switch-android-2_1.12.xx/1/execution/node/144/log/.

12:16:11  Cannot contact i-069b2c55a26d28b9b: hudson.remoting.RequestAbortedException: java.io.IOException: Unexpected termination of the channel
12:21:12  Could not connect to i-069b2c55a26d28b9b to send interrupt signal to process

[kjozwiak]

@emerick mind fixing the above conflict? Assuming it happened when we merged #6354 (review).

[kjozwiak]

Uplift into 1.12.x approved after deliberating with @brave/uplift-approvers. QA has also verified that rewards staging is working on Nightly as per #6267 (comment).