Problems panel shows problems in virtual and read only file

**Describe the bug**

The problems panel is showing problems in a virtual and read only file:

When I copy the problem and paste the contents into a new file, I see this:

```
"resource": "/commit~cf17f9d0/.github/workflows/build.yml",
"owner": "_generated_diagnostic_collection_name_#3",
```

`/commit~cf17f9d0/.github/workflows/build.yml` is not a real file (at least not in my project's directory).

When I click on one of these problems to open the file and then I try to make changes, VS Code reports that it's a read only file:

The problems disappear when I uninstall or disable the extension.

The problems re-appear when I re-install or re-enable the extension.

**To Reproduce**
Unfortunately I don't have steps to reproduce this. I'm not sure how it happened.

**Expected behavior**
Problems should only appear for real files.

**Screenshots**
See above.

**Extension Version**
`v0.25.7`

**Additional context**

まず、報告された `/commit~cf17f9d0/.github/workflows/build.yml` リソースを例として使用し、拡張機能が VS Code の Problems パネルにどのように診断情報を提供しているかを調査します。拡張機能を有効にした場合と無効にした場合の動作を比較し、診断情報が実在する編集可能なファイルに対してのみ表示されることを確認する方法を明らかにします。

索引モデルが issue の本文から書いたものです。