fix(deps): update module github.com/prometheus/client_golang to v1.21.1

Author: renovate[bot]

go.mod

@@ -5,7 +5,7 @@ go 1.19
 require (
 	github.com/alecthomas/kingpin/v2 v2.3.2
 	github.com/go-kit/log v0.2.1
-	github.com/prometheus/client_golang v1.16.0
+	github.com/prometheus/client_golang v1.21.1
 	github.com/prometheus/common v0.44.0
 	github.com/prometheus/exporter-toolkit v0.10.0
 	github.com/stretchr/testify v1.8.4