fix: fix keyword completion for dialects

[ap891843]

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
  - Install IDMS extension.
  - Provide IDMS as a dialect for a workspace in settings.json.
  - Trigger suggestion on a COBOL file (ctrl + space).
  - Verify that IDMS-STATISTICS is present in the list.

Checklist:

• Each my commit contains one meaningful change
• I have performed rebase my branch on top of development
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have checked my code and corrected any misspellings