Address some CodeQL security concerns (#35572)

Although there is no real security problem

routers/web/repo/githttp.go

@@ -376,7 +376,7 @@ func (h *serviceHandler) sendFile(ctx *context.Context, contentType, file string
 		ctx.Resp.WriteHeader(http.StatusBadRequest)
 		return
 	}
-	reqFile := filepath.Join(h.getRepoDir(), file)
+	reqFile := filepath.Join(h.getRepoDir(), filepath.Clean(file))
 
 	fi, err := os.Stat(reqFile)
 	if os.IsNotExist(err) {
@@ -395,13 +395,12 @@ func (h *serviceHandler) sendFile(ctx *context.Context, contentType, file string
 var safeGitProtocolHeader = regexp.MustCompile(`^[0-9a-zA-Z]+=[0-9a-zA-Z]+(:[0-9a-zA-Z]+=[0-9a-zA-Z]+)*$`)
 
 func prepareGitCmdWithAllowedService(service string) (*gitcmd.Command, error) {
-	if service == "receive-pack" {
-		return gitcmd.NewCommand("receive-pack"), nil
+	if service == ServiceTypeReceivePack {
+		return gitcmd.NewCommand(ServiceTypeReceivePack), nil
 	}
-	if service == "upload-pack" {
-		return gitcmd.NewCommand("upload-pack"), nil
+	if service == ServiceTypeUploadPack {
+		return gitcmd.NewCommand(ServiceTypeUploadPack), nil
 	}
-
 	return nil, fmt.Errorf("service %q is not allowed", service)
 }
 
@@ -464,11 +463,16 @@ func serviceRPC(ctx *context.Context, h *serviceHandler, service string) {
 	}
 }
 
+const (
+	ServiceTypeUploadPack  = "upload-pack"
+	ServiceTypeReceivePack = "receive-pack"
+)
+
 // ServiceUploadPack implements Git Smart HTTP protocol
 func ServiceUploadPack(ctx *context.Context) {
 	h := httpBase(ctx)
 	if h != nil {
-		serviceRPC(ctx, h, "upload-pack")
+		serviceRPC(ctx, h, ServiceTypeUploadPack)
 	}
 }
 
@@ -476,16 +480,18 @@ func ServiceUploadPack(ctx *context.Context) {
 func ServiceReceivePack(ctx *context.Context) {
 	h := httpBase(ctx)
 	if h != nil {
-		serviceRPC(ctx, h, "receive-pack")
+		serviceRPC(ctx, h, ServiceTypeReceivePack)
 	}
 }
 
 func getServiceType(ctx *context.Context) string {
-	serviceType := ctx.Req.FormValue("service")
-	if !strings.HasPrefix(serviceType, "git-") {
-		return ""
+	switch ctx.Req.FormValue("service") {
+	case "git-" + ServiceTypeUploadPack:
+		return ServiceTypeUploadPack
+	case "git-" + ServiceTypeReceivePack:
+		return ServiceTypeReceivePack
 	}
-	return strings.TrimPrefix(serviceType, "git-")
+	return ""
 }
 
 func updateServerInfo(ctx gocontext.Context, dir string) []byte {