fix: Various sec fixes (#38108) (#38147)

Backport #38108

- Enforce repository token scope on RSS/Atom feed endpoints so a PAT
without repo scope can no longer read private repo commit data.
- Block HTTP redirects during repository migration clones to prevent
SSRF reaching internal addresses via an attacker-controlled redirect.
- Redact the notification subject after repo access is revoked so
private issue/PR metadata is no longer leaked through the notification
API.

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/git/repo.go

@@ -121,6 +121,9 @@ func Clone(ctx context.Context, from, to string, opts CloneRepoOptions) error {
 	}
 
 	cmd := gitcmd.NewCommand().AddArguments("clone")
+	// Never follow HTTP redirects: no clone caller needs them, and a remote redirecting to an
+	// otherwise-blocked address would be an SSRF vector (e.g. migrating from an attacker URL).
+	cmd.AddArguments("-c", "http.followRedirects=false")
 	if opts.SkipTLSVerify {
 		cmd.AddArguments("-c", "http.sslVerify=false")
 	}