[BUG] `along with GitHub Advanced Security on private repositories` is superfluous for public repositories

[jsoref]

Describe the bug
Error message mentions private repositories, but the action can know that the repository in question is not private.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://github.com/check-spelling-sandbox/caffeine/actions/runs/14451650273/job/40525556101?pr=1#step:5:9
2. See

   Error: Dependency review is not supported on this repository. Please ensure that Dependency graph is enabled along with GitHub Advanced Security on private repositories, see https://github.com/check-spelling-sandbox/caffeine/settings/security_analysis

Expected behavior
If a fact can be known, don't mention the opposite

Screenshots

Action version
What version of the action are you using in your workflow? ce3cf95

Note: if you're not running the latest release please try that first!

The code is still present in the current version:

dependency-review-action/src/main.ts

Line 199 in 67d4f4b

`Dependency review is not supported on this repository. Please ensure that Dependency graph is enabled along with GitHub Advanced Security on private repositories, see ${github.context.serverUrl}/${github.context.repo.owner}/${github.context.repo.repo}/settings/security_analysis`

Examples
https://github.com/check-spelling-sandbox/caffeine/actions/runs/14451650273/workflow?pr=1

Additional context
GitHub exposes github.event.repository.private:
https://github.com/jsoref/debug-github-events/actions/runs/14014253846

... so this code could check for that and private a better message.