go.toolchain.rev: bump to Go 1.26.4

Updates https://github.com/tailscale/corp/issues/42772
Updates https://github.com/tailscale/tailscale/issues/19982

Signed-off-by: Mario Minardi <mario@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f