Add branch+commit to "What to Test" field in TestFlight.

Adds the branch and last commit to the "What to Test" field in TestFlight to more easily determine the version of each available option in your TestFlight is.

fastlane/Fastfile

@@ -156,6 +156,7 @@ platform :ios do
       skip_submission: false,
       ipa: "Loop.ipa",
       skip_waiting_for_build_processing: true,
+      changelog: git_branch+" "+last_git_commit[:abbreviated_commit_hash],
     )
   end