fix: Updating the node environment to Node.js 20

[iennae]

Description

updates some region tags, updates node environment

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• [] Tests pass: npm test (see Testing)
• [] Lint pass: npm run lint (see Style)
• This pull request is from a branch created directly off of GoogleCloudPlatform/nodejs-docs-samples. Not a fork.
• Please merge this PR for me once it is approved

I verified that the changes worked (region tags don't impact deployment)

[snippet-bot]

Here is the summary of changes.

You are about to add 6 region tags.

• appengine/building-an-app/build/app.yaml:15, tag gae_app_yaml
• appengine/building-an-app/build/server.js:18, tag gae_app
• appengine/building-an-app/update/server.js:18, tag gae_update_app
• appengine/building-an-app/update/server.js:25, tag gae_enable_parser
• appengine/building-an-app/update/server.js:36, tag gae_add_display_form
• appengine/building-an-app/update/server.js:44, tag gae_add_post_handler

You are about to delete 5 region tags.

• appengine/twilio/app.flexible.yaml:17, tag gae_flex_twilio_env
• appengine/twilio/app.js:41, tag gae_flex_twilio_receive_call
• appengine/twilio/app.js:51, tag gae_flex_twilio_send_sms
• appengine/twilio/app.js:75, tag gae_flex_twilio_receive_sms
• appengine/twilio/app.standard.yaml:16, tag gae_twilio_env

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[pattishin]

/gcbrun

[pattishin]

Thanks @iennae! 👍🏼 Added a few comments based from snippet-bot and header-check.