Update xunit-dotnet monorepo

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
xunit	2.6.3 -> 2.6.4
xunit.runner.visualstudio	2.5.5 -> 2.5.6

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Release Notes

xunit/xunit (xunit)

### [`v2.6.4`](https://togithub.com/xunit/xunit/compare/2.6.3...2.6.4) [Compare Source](https://togithub.com/xunit/xunit/compare/2.6.3...2.6.4)

xunit/visualstudio.xunit (xunit.runner.visualstudio)

### [`v2.5.6`](https://togithub.com/xunit/visualstudio.xunit/compare/2.5.5...2.5.6) [Compare Source](https://togithub.com/xunit/visualstudio.xunit/compare/2.5.5...2.5.6)

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Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

👻 Immortal: This PR will be recreated if closed unmerged. Get config help if that's undesired.

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• [ ] If you want to rebase/retry this PR, check this box

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