Update all non-major dependencies Docker tags (patch)

This MR contains the following updates:

Package	Type	Update	Change
docker	service-image	patch	20.10.19-dind -> 20.10.21-dind
docker	image	patch	20.10.19 -> 20.10.21
github.com/stretchr/testify	require	patch	v1.8.0 -> v1.8.1
golangci/golangci-lint	image	patch	v1.50.0-alpine -> v1.50.1-alpine

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Release Notes

stretchr/testify

v1.8.1

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