bug: a `!reference` tag anywhere in the file suppresses all input completion

[X-Guardian]

Bug summary

!reference [.job, key] is GitLab's own YAML tag for splicing another job's key into the current one. It belongs to no YAML schema, so js-yaml throws unknown sequence tag !<!reference> when it hits one. The throw is caught and the parse returns null/[], which takes down the entire file — the include: block included — even though the tag sits in an unrelated job further down. The completion, hover, and validation providers then see no include: and silently do nothing.

!reference is common in real pipelines (it is the standard way to reuse a .setup-style hidden job's script), so any file using one loses input completion entirely.

Steps to reproduce

1. Open a .gitlab-ci.yml with an include: entry carrying an inputs: block, and a later job using - !reference [.some-job, script] (see the snippet below).
2. Put the cursor on a blank, correctly-indented line inside that include's inputs: block.
3. Request input-name completion (Ctrl+Space).

Expected behavior

• Input-name completions are offered for the include's not-yet-set inputs. The !reference tag is in an unrelated job and should have no bearing on the include: block.

Actual behavior

• No completions are offered. The debug log shows No inputs parameter-name slot at cursor.
• Deleting the - !reference [.pnpm-setup, script] line makes completions work immediately — confirming the tag is the trigger.

Component context (if applicable)

Component URL: n/a (reproduces with local: and component: includes)
GitLab instance: n/a
Project path: n/a
Version/reference: n/a
Source type: local include / component

Minimal .gitlab-ci.yml snippet

include:
  - component: $CI_SERVER_FQDN/my-group/my-project/my-component@1.0.0
    inputs:
      # cursor on the blank line here — no completions offered before the fix

.pnpm-setup:
  script:
    - corepack enable
    - pnpm install --frozen-lockfile

test:
  script:
    - !reference [.pnpm-setup, script]
    - pnpm test

Extension logs

N/A

Affected area

Completion provider

Extension version

0.16.2

VS Code version

1.128.0

Node.js version

22.x

Operating system

macOS

Pre-submit checks

• I searched existing issues and did not find a duplicate.
• I can reproduce this on the latest version from main/beta.
• I included a minimal YAML snippet and relevant logs.