Open the sync pull request straight from ankidroid:main

[float3]

• Open the sync pull request straight from ankidroid:main #54 merged the earlier version, which recreates main; this is the rewrite
• no main branch in the fork: the job checks out ankiquest, fetches ankidroid/Anki-Android main, and if ankiquest is behind opens a PR with head ankidroid:main (skips if one is open)
• REST API instead of gh pr create, whose --head owner:branch does not support organizations
• nothing is pushed, so UPSTREAM_SYNC_TOKEN only needs pull request access; still a PAT so the PR's CI runs
• main gets deleted again after this merges

[github-actions]

Snapshot diff report vs ankiquest. Open screenshot-diff for diffs.

• AnkiquestHomeScreenshotTest: 1 change
• ChangeNoteTypeDialogScreenshotTest: 4 changes
• InsertFieldDialogScreenshotTest: 8 changes
• SyncClockErrorScreenshotTest: 1 change

All 14 changed screenshots

AnkiquestHomeScreenshotTest

• today_320dp_compare.png

ChangeNoteTypeDialogScreenshotTest

• gesture_navigation_compare.png
• landscape_compare.png
• portrait_compare.png
• portrait_cutout_compare.png

InsertFieldDialogScreenshotTest

• gesture_navigation_compare.png
• gesture_navigation_special_scrolled_to_bottom_compare.png
• landscape_compare.png
• landscape_special_scrolled_to_bottom_compare.png
• portrait_compare.png
• portrait_cutout_compare.png
• portrait_cutout_special_scrolled_to_bottom_compare.png
• portrait_special_scrolled_to_bottom_compare.png

SyncClockErrorScreenshotTest

• clock_error_dialog_compare.png