fix(NODE-6381): use targeting for x86_64 darwin

[durran]

Description

Fixes native build for darwin-x86_64

What is changing?

• Updates the npm build steps in CI fr x86_64 to specifically target that platform.
• Updates download artifact actions to latest v4, since v2 was removed.

Is there new documentation needed for these changes?

None

What is the motivation for this change?

Broken installs for 1.2.1 on darwin x86_64

Double check the following

• Ran npm run format:js && npm run format:rs script
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket