Fix GDTCCTUploader-upload Crash

[paulb777]

Analysis from @ncooke3:

I'm pretty confident that this PR is valid code cleanup, but won't actually fix the crash.

Here's the order of events:

• Background task is created (line 134)
• App is backgrounded and the system starts a 30 second timer to complete in-progress background tasks
• 30 second timer runs out, warning is issued if unfinished background tasks exist
• A grace period is given (non-deterministic, few seconds long) before the system kills the app (because the app is backgrounded, the user will experience a fresh app launch)

Gemini's summary:

Summary

The expirationHandler for the background task was attempting to cancel a non-existent currentTask property. This meant that if an upload task timed out, the operation would never be cancelled, and the background task identifier would never be released, leading to a warning from the OS and potential termination of the app.

The fix replaces the incorrect call with [self cancel], which correctly triggers the NSOperation's cancellation mechanism. This ensures that the operation terminates gracefully, allowing its promise chain to clean up and properly end the background task.

The CHANGELOG.md has also been updated to reflect this fix.

[google-oss-bot]

Coverage Report ¹

Affected Products

No changes between base commit (5a9a019) and merge commit (f6dbd63).

Test Logs

• Base (5a9a019): https://github.com/google/GoogleDataTransport/actions/runs/17812398842
• Merge (f6dbd63): https://github.com/google/GoogleDataTransport/actions/runs/20045056375

1. https://storage.googleapis.com/firebase-sdk-metric-reports/llR2AWdGnt.html

[ncooke3]

firebase/firebase-ios-sdk#15129 is a different background task so this doesn't fix that one.

[ncooke3]

Will come back to this. Looks like the dead property was created in #3.