Bump vitess.io/vitess from 0.16.2 to 0.17.7 in /vitess-mixin (#15918)

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

vitess-mixin/go.mod

@@ -13,8 +13,8 @@ require (
 	// Believe it or not, this is actually version 2.13.1
 	// See https://github.com/prometheus/prometheus/issues/5590#issuecomment-546368944
 	github.com/prometheus/prometheus v1.8.2-0.20191017095924-6f92ce560538
-	github.com/stretchr/testify v1.8.1
-	vitess.io/vitess v0.16.2
+	github.com/stretchr/testify v1.8.3
+	vitess.io/vitess v0.17.7
 )
 
 replace k8s.io/client-go v2.0.0-alpha.0.0.20181121191925-a47917edff34+incompatible => k8s.io/client-go v2.0.0-alpha.1+incompatible