.NET global tools are no longer being updated

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Package ecosystem

NuGet

### Package manager version

_No response_

### Language version

_No response_

### Manifest location and content before the Dependabot update

https://github.com/App-vNext/Polly/blob/708b02b0a6e4721103f6115c7fcc38acbef05103/.config/dotnet-tools.json

### dependabot.yml content

https://github.com/App-vNext/Polly/blob/main/.github/dependabot.yml

### Updated dependency

None.

### What you expected to see, versus what you actually saw

Dependabot should have generated PRs to update the following tools:

- dotnet-stryker 4.7.0 ➡️ 4.8.0
- MartinCostello.WaitForNuGetPackage 1.1.0 ➡️ 1.1.2
- sign 0.9.1-beta.25228.1 ➡️ 0.9.1-beta.25379.1

The last PR we had that updated a tool was on May 1st: https://github.com/App-vNext/Polly/pull/2608

### Native package manager behavior

_No response_

### Images of the diff or a link to the PR, issue, or logs

https://github.com/App-vNext/Polly/actions/runs/17159446769/job/48684648621

### Smallest manifest that reproduces the issue

_No response_

Start by comparing the repository's .config/dotnet-tools.json manifest with .github/dependabot.yml, then inspect the linked GitHub Actions run and the NuGet/.NET global-tools handling in Dependabot. Done means identifying why these tools are skipped and confirming that updates for dotnet-stryker, MartinCostello.WaitForNuGetPackage, and sign can generate PRs.

Written by the indexing model from the issue text.