Variable assignment breaks doc splitting

[Angivare]

Describe the bug

split_doc does not split documents anymore after a variable assignment.

Version of yq: 4.44.2
Operating system: Linux (WSL)
Installed via: binary release

Input Yaml
Concise yaml document(s) (as simple as possible to show the bug, please keep it to 10 lines or less)
data1.yml:

[1, 2]

Command
The command you ran:

echo '[1, 2]' | yq '.[] | . as $_ | split_doc'

Actual behavior

1
2

Expected behavior

1
---
2

Additional context

The ran command should really be equivalent to

echo '[1, 2]' | yq '.[] | split_doc'

which does give the expected output.