chore: Upgrade visual resgression script to node 20

[michaeldowseza]

Description

Update actions node version to explicitly node version 20 as node 18 is out of active support.

Related links, issue #, if available: n/a

AWSUI-59859

How has this been tested?

PR checks make use of the code change. Can verify below.

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.98%. Comparing base (ea82360) to head (fa99c2a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #25   +/-   ##
=======================================
  Coverage   96.98%   96.98%           
=======================================
  Files          16       16           
  Lines         398      398           
  Branches       26       26           
=======================================
  Hits          386      386           
  Misses         12       12           

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