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/github.com/cespare/xxhash/v2/xxhash_unsafe.go

@@ -1,3 +1,4 @@
+//go:build !appengine
 // +build !appengine
 
 // This file encapsulates usage of unsafe.
@@ -11,7 +12,7 @@ import (
 
 // In the future it's possible that compiler optimizations will make these
 // XxxString functions unnecessary by realizing that calls such as
-// Sum64([]byte(s)) don't need to copy s. See https://golang.org/issue/2205.
+// Sum64([]byte(s)) don't need to copy s. See https://go.dev/issue/2205.
 // If that happens, even if we keep these functions they can be replaced with
 // the trivial safe code.