Chore(deps): Bump github.com/prometheus/client_golang (#30585)

Bumps [github.com/prometheus/client_golang](https://github.com/prometheus/client_golang) from 1.8.0 to 1.9.0.
- [Release notes](https://github.com/prometheus/client_golang/releases)
- [Changelog](https://github.com/prometheus/client_golang/blob/master/CHANGELOG.md)
- [Commits](https://github.com/prometheus/client_golang/compare/v1.8.0...v1.9.0)

Signed-off-by: dependabot[bot] <support@github.com>

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

go.mod

@@ -63,7 +63,7 @@ require (
 	github.com/opentracing/opentracing-go v1.2.0
 	github.com/patrickmn/go-cache v2.1.0+incompatible
 	github.com/pkg/errors v0.9.1
-	github.com/prometheus/client_golang v1.8.0
+	github.com/prometheus/client_golang v1.9.0
 	github.com/prometheus/client_model v0.2.0
 	github.com/prometheus/common v0.15.0
 	github.com/robfig/cron v0.0.0-20180505203441-b41be1df6967
@@ -84,7 +84,6 @@ require (
 	golang.org/x/net v0.0.0-20201022231255-08b38378de70
 	golang.org/x/oauth2 v0.0.0-20200902213428-5d25da1a8d43
 	golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9
-	golang.org/x/sys v0.0.0-20201022201747-fb209a7c41cd // indirect
 	golang.org/x/time v0.0.0-20200630173020-3af7569d3a1e
 	gonum.org/v1/gonum v0.6.0
 	google.golang.org/api v0.33.0