Reproduction steps:
1. Open the attached “IN-94285” project
2. In the Assets folder open the “Testingg” Animation Clip
3. Resize the window so it has both the vertical and horizontal scroll bars
4. In the Animation window select the Dopesheet
5. In the Dopesheet hold the middle mouse button and scroll horizontally, then vertically
6. Observe the Animation window

Expected result: The Dopesheet scrolls both horizontally and vertically
Actual result: The Dopesheet scrolls only vertically

Reproducible with: 2021.3.48f1, 2022.3.57f1, 6000.0.37f1, 6000.1.0a5, 6000.2.0a2

Reproducible on: Windows 11
Not reproducible on: No other environments tested