Update testcontainers-dotnet monorepo to 4.8.1

This MR contains the following updates:

Package	Change	Age	Confidence
Testcontainers.Redis (source)	4.8.0 -> 4.8.1
Testcontainers.Xunit (source)	4.8.0 -> 4.8.1

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Release Notes

testcontainers/testcontainers-dotnet (Testcontainers.Redis)

v4.8.1

Compare Source

What's Changed

🐛 Bug Fixes

• fix: Compute correct relative Dockerfile file path (#​1558) @​HofmeisterAn

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