fix: support HEAD requests on Alpine registry APKINDEX.tar.gz (#38686) (#38688)

Backport #38686 by @waterWang

### Description

Fixes #38676

The Alpine package registry registers for only, so a request returns .
Clients that probe the index with before fetching it (like and other
-based tools) fail outright.

**Fix:** Change to for the APKINDEX.tar.gz route, matching the pattern
already used by the i386 registry a few lines below.

### Related issue

Closes #38676

Co-authored-by: water <672684719@qq.com>
Co-authored-by: waterWang <waterWang@users.noreply.github.com>

routers/api/packages/api.go

@@ -135,7 +135,7 @@ func CommonRoutes() *web.Router {
 			r.Group("/{branch}/{repository}", func() {
 				r.Put("", reqPackageAccess(perm.AccessModeWrite), alpine.UploadPackageFile)
 				r.Group("/{architecture}", func() {
-					r.Get("/APKINDEX.tar.gz", alpine.GetRepositoryFile)
+					r.Methods("HEAD,GET", "/APKINDEX.tar.gz", alpine.GetRepositoryFile)
 					r.Group("/{filename}", func() {
 						r.Get("", alpine.DownloadPackageFile)
 						r.Delete("", reqPackageAccess(perm.AccessModeWrite), alpine.DeletePackageFile)