Merge key with inline map broken

[stevenwdv]

Describe the bug
When I use a merge key (<<:) with an inline map rather than an anchor, yq doesn't propagate keys to the parent map.

Version of yq: 4.45.4
Operating system: linux
Installed via: binary release

Input Yaml
data1.yml:

dummy: 42
<<:
  foo: 123

Command

yq eval '.bar' data1.yml
yq eval 'explode(.)' data1.yml

Actual behavior

.bar:

null

explode(.):

dummy: 42

Expected behavior

.bar:

123

explode(.):

dummy: 42
foo: 123

Additional context
Other YAML parsers seem fine with this, e.g. PyYAML (and online tools: https://www.yamllint.com/, https://jsonformatter.org/yaml-to-json). See also the spec.

I encountered this problem when implementing a custom !include tag using load(.), where exploding <<: !include "file.yml" wouldn't work.