Read-only editors for action.yml shows problems as if it were a workflow

[MetRonnie]

Describe the bug

Some diffs (but not all!) show a load of false positive Problems for action.yml treating it as if it were a workflow YAML file.

Possibly this only affects read-only diffs.

To Reproduce
Steps to reproduce the behavior:

1. Open a read-only diff of an action.yml file

Expected behavior
action.yml should be correctly identified as an action not a workflow, in diff views

Screenshots

Top: an unaffected diff; bottom: an affected read-only diff

Extension Version
0.32.3

Additional context
(Originally opened in microsoft/vscode-pull-request-github#8873 but it affects diffs unrelated to PRs)

[MetRonnie]

Looks like this affects any read-only editor, not just diffs