rebase: bump github.com/prometheus/client_golang from 1.14.0 to 1.15.1

Bumps [github.com/prometheus/client_golang](https://github.com/prometheus/client_golang) from 1.14.0 to 1.15.1.
- [Release notes](https://github.com/prometheus/client_golang/releases)
- [Changelog](https://github.com/prometheus/client_golang/blob/main/CHANGELOG.md)
- [Commits](https://github.com/prometheus/client_golang/compare/v1.14.0...v1.15.1)

---
updated-dependencies:
- dependency-name: github.com/prometheus/client_golang
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

vendor/golang.org/x/oauth2/internal/token.go

@@ -19,8 +19,6 @@ import (
 	"strings"
 	"sync"
 	"time"
-
-	"golang.org/x/net/context/ctxhttp"
 )
 
 // Token represents the credentials used to authorize
@@ -229,7 +227,7 @@ func RetrieveToken(ctx context.Context, clientID, clientSecret, tokenURL string,
 }
 
 func doTokenRoundTrip(ctx context.Context, req *http.Request) (*Token, error) {
-	r, err := ctxhttp.Do(ctx, ContextClient(ctx), req)
+	r, err := ContextClient(ctx).Do(req.WithContext(ctx))
 	if err != nil {
 		return nil, err
 	}