[landing] fix the scroll to top behavior and animation on keyserver page

Summary:
This diff fixes both the scroll to top behavior and the animations on the keyserver page. The overflow property here was causing issues with the scroll behavoir (which is why the scroll animation and the scroll to top was not working)

Depends on D8174

Test Plan:
Please see the demo videos below to see that both things now work

Reviewers: atul, kamil

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8175