chore(deps): update actions/setup-node action to v6

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
actions/setup-node	action	major	v4 -> v6

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Release Notes

actions/setup-node (actions/setup-node)

v6

Compare Source

v5

Compare Source

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Configuration

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[github-actions]

@launchdarkly/browser size report
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Compressed size: 169118 bytes
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Uncompressed size: 789399 bytes

[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
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Compressed size limit: 26000
Uncompressed size: 122411 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 17636 bytes
Compressed size limit: 20000
Uncompressed size: 90259 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 21721 bytes
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Uncompressed size: 74698 bytes

[jsonbailey]

I created a PR to have renovate use digests instead of tags. We may want to review that before deciding if we want to merge this #955