Run action with NodeJS 16

[der-eismann]

Description

As mentioned in #24 (comment) the action itself still runs on NodeJS 12, while it is built/tested with NodeJS 16. Let's push everything to 16, just like other actions did.
Unfortunately this is seen as a breaking change because it is incompatible with GitHub Enterprise Server <= 3.3.

Checklist

• This PR includes a documentation change
• This PR does not need a documentation change

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• This PR includes test changes
• This PR's changes are already tested

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• This change is not user-facing
• This change is a patch change
• This change is a minor change
• This change is a major (breaking) change

Changes made

• Changed action so it runs on node16
• Changed package.json so it requests node16

[ssbarnea]

Can we revive this, Github already deprecated all actions using node 12 and there are warnings on all builds using actions based on node 12.