TF-4269 Fix Sentry dSYM upload: find xcarchive via find instead of gym_archive_path.txt

lane_context[XCODEBUILD_ARCHIVE] was unreliable — replace with find on
~/Library/Developer/Xcode/Archives to locate the Runner xcarchive directly.

ios/.gitignore

@@ -26,9 +26,6 @@ ServiceDefinitions.json
 Runner/GeneratedPluginRegistrant.*
 Flutter/ephemeral/
 
-# Build artifacts generated by Fastlane
-gym_archive_path.txt
-
 # Exceptions to above rules.
 !default.mode1v3
 !default.mode2v3

ios/fastlane/Fastfile

@@ -56,10 +56,6 @@ platform :ios do
       workspace: "Runner.xcworkspace",
       export_method: "app-store"
     )
-    # Write the xcarchive path to a file so CI can locate dSYMs for Sentry upload.
-    # lane_context[XCODEBUILD_ARCHIVE] is set by build_app and contains the exact path.
-    archive_path = Actions.lane_context[SharedValues::XCODEBUILD_ARCHIVE]
-    File.write("gym_archive_path.txt", archive_path.to_s) if archive_path
     upload_to_testflight(
       skip_waiting_for_build_processing: true,
       ipa: "Runner.ipa"