[cssom-view] Correct indentation for "run the scroll steps"

[AtkinsSJ]

These substeps were indented by 2 spaces, which Bikeshed didn't interpret as being nested, but was placing them at the same level. Indenting the steps by 4 spaces instead corrects the HTML output.

This is an editorial change, purely whitespace.

To illustrate, before:

And after:

[w3cbot]

nt1m marked as non substantive for IPR from ash-nazg.