`Missing download info for` message could be more helpful

Describe the bug
When you specify a uses: some/action@non-existent-ref-name, the error message isn't terribly helpful

https://github.com/actions/runner/blob/a0a0a76378ad3ce3745fbf27f69cafc506e4ed00/src/Runner.Worker/ActionManager.cs#L212

To Reproduce

1. Create and run a workflow that uses an action with a reference to a ref name that doesn't exist, https://github.com/check-spelling-sandbox/onedrive/actions/runs/14161440115)
2. See error

Expected behavior
Error message should suggest,

• if the repository exists, that it's likely the reference name is bad.
• if no public repository exists and the owner doesn't match the current repository's owner, that "either the repository doesn't exist, or it's private and that you cannot use private repositories in uses:"
• if no public repository exists and the owner does match the current repository's owner, that "either the repository doesn't exist, or it's private and you haven't set the repository to be used, but you could..."

Runner Version and Platform

Version of your runner?
2.323.0

OS of the machine running the runner? Ubuntu 24.04.2

What's not working?

Please include error messages and screenshots.

Getting action download info
Error: Missing download info for check-spelling-sandbox/check-spelling@prereleae

Job Log Output

If applicable, include the relevant part of the job / step log output here. All sensitive information should already be masked out, but please double-check before pasting here.

Runner and Worker's Diagnostic Logs

Start at src/Runner.Worker/ActionManager.cs around line 212 and reproduce the workflow using a nonexistent action reference. Update the error wording to distinguish a bad reference, an unavailable repository, and the owner-specific private-repository cases described in the issue; done means the resulting message is more helpful for each scenario.