chore: Update go.mod to include testify v1.9.0

[ShocOne]

This commit updates the go.mod file to include the testify v1.9.0 package as a direct dependency. This is necessary for the upcoming changes that will utilize the testify library for writing tests and asserting conditions. By explicitly adding the testify package, we ensure that the correct version is used and avoid any potential conflicts with indirect dependencies.

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