Coverage report does not include .vue files when the all option is set

* **Version**: v7.11.0

### System Info

```shell
System:
OS: macOS 11.6.2
CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
Memory: 192.20 MB / 32.00 GB
Shell: 5.8 - /bin/zsh
Binaries:
Node: 16.13.2 - ~/.nvm/versions/node/v16.13.2/bin/node
Yarn: 1.22.17 - ~/.nvm/versions/node/v16.13.2/bin/yarn
npm: 8.1.2 - ~/.nvm/versions/node/v16.13.2/bin/npm
Browsers:
Chrome: 98.0.4758.80
Firefox: 96.0.2
Firefox Developer Edition: 97.0
Safari: 15.2
Safari Technology Preview: 15.4
npmPackages:
@vitejs/plugin-vue: ^2.1.0 => 2.1.0
vitest: latest => 0.2.7
```

When running `vitest` (uses c8 internally) with the `coverage` `all: true` option set, uncovered `.vue` files are not included in coverage results.
Related issue: https://github.com/vitest-dev/vitest/issues/680
Reproduction repo: https://github.com/kouts/vitest-coverage