chore: update snyk workflow to use node20

[dbumblis-parabol]

Description

Updates deprecated actions used within workflow to v4 - node20

Demo

N/A

Testing scenarios

Action runs without deprecation warnings

Final checklist

• I checked the code review guidelines
• I have added Metrics Representative as reviewer(s) if my PR invovles metrics/data/analytics related changes
• I have performed a self-review of my code, the same way I'd do it for any other team member
• I have tested all cases I listed in the testing scenarios and I haven't found any issues or regressions
• Whenever I took a non-obvious choice I added a comment explaining why I did it this way
• I added the label Skip Maintainer Review Indicating the PR only requires reviewer review and can be merged right after it's approved if the PR introduces only minor changes, does not contain any architectural changes or does not introduce any new patterns and I think one review is sufficient'
• PR title is human readable and could be used in changelog

[mattkrick]

i just merged blindly because I had to do a similar upgrade for another CI test & there's no convenient way to test it other than merging right to master