workhorse: Update module github.com/stretchr/testify to v1.8.4

This MR contains the following updates:

Package	Type	Update	Change
github.com/stretchr/testify	require	patch	v1.8.3 -> v1.8.4

MR created with the help of gitlab-org/frontend/renovate-gitlab-bot

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Release Notes

stretchr/testify

v1.8.4

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