Add serviceworker.js to KnownPublicEntries (#11992)

Fixes a wrong 302 redirect to the login page, see https://github.com/go-gitea/gitea/issues/11989.
Also made it so the reserved username list is extended with those known
entries so we avoid code duplication.

Should be backported to 1.12.

modules/public/public.go

@@ -30,12 +30,13 @@ type Options struct {
 	Prefix       string
 }
 
-// List of known entries inside the `public` directory
-var knownEntries = []string{
+// KnownPublicEntries list all direct children in the `public` directory
+var KnownPublicEntries = []string{
 	"css",
 	"fomantic",
 	"img",
 	"js",
+	"serviceworker.js",
 	"vendor",
 }
 
@@ -114,7 +115,7 @@ func (opts *Options) handle(ctx *macaron.Context, log *log.Logger, opt *Options)
 			if len(parts) < 2 {
 				return false
 			}
-			for _, entry := range knownEntries {
+			for _, entry := range KnownPublicEntries {
 				if entry == parts[1] {
 					ctx.Resp.WriteHeader(404)
 					return true