Wrap blog public notices use of VIP_GO_APP_ENVIRONMENT in a defined check

[brandon-m-skinner]

Description

The new notice that your non-production site might be indexable by search engines throws a warning in CI and likely other places outside VIP Go where VIP_GO_APP_ENVIRONMENT isn't defined.

This PR wraps the usage of VIP_GO_APP_ENVIRONMENT in a defined check to avoid the warning and future error.

Changelog Description

Bug Fix: Fix warning thrown by blogpublic-notice.php when VIP_GO_APP_ENVIRONMENT isn't defined

We wrapped the usage of VIP_GO_APP_ENVIRONMENT in a defined check so it won't throw warnings anymore.

Checklist

Please make sure the items below have been covered before requesting a review:

• This change works and has been tested locally (or has an appropriate fallback).
• This change works and has been tested on a Go sandbox.
• This change has relevant unit tests (if applicable).
• This change has relevant documentation additions / updates (if applicable).
• I've created a changelog description that aligns with the provided examples.

Steps to Test

1. Run anything without VIP_GO_APP_ENVIRONMENT defined.
2. Note the undefined constant warning.
3. Apply the PR.
4. Do 1 again.
5. There shouldn't be an undefined constant warning anymore.

[brandon-m-skinner]

r1396-stacks