Fix test delivery button in repo webhook settings page (#24478)

Caused by
https://github.com/go-gitea/gitea/pull/24246/files#diff-2bfe41d93dbb409583a4f945902e46bb513f60f1c9301649c1689200c4f1466eR1

Class `new` was removed in #24246, but in function
`initCompWebHookEditor`, it will check `.new.webhook`.
So in repo webhook settings page, `initCompWebHookEditor` will init
nothing, and no response after click the test delivery button.

da65b7ad47/web_src/js/features/comp/WebHookEditor.js (L6-L9)

Co-authored-by: Giteabot <teabot@gitea.io>

templates/repo/settings/webhook/new.tmpl

@@ -1,4 +1,4 @@
-{{template "repo/settings/layout_head" (dict "ctxData" . "pageClass" "repository settings webhook")}}
+{{template "repo/settings/layout_head" (dict "ctxData" . "pageClass" "repository settings new webhook")}}
 	<div class="repo-setting-content">
 		<h4 class="ui top attached header">
 			{{if .PageIsSettingsHooksNew}}{{.locale.Tr "repo.settings.add_webhook"}}{{else}}{{.locale.Tr "repo.settings.update_webhook"}}{{end}}