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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workhorse/go.mod

@@ -25,7 +25,7 @@ require (
 	github.com/sebest/xff v0.0.0-20210106013422-671bd2870b3a
 	github.com/sirupsen/logrus v1.9.0
 	github.com/smartystreets/goconvey v1.7.2
-	github.com/stretchr/testify v1.8.3
+	github.com/stretchr/testify v1.8.4
 	gitlab.com/gitlab-org/gitaly/v16 v16.0.1
 	gitlab.com/gitlab-org/labkit v1.18.0
 	gocloud.dev v0.29.0