fix hcloud-csi.yaml if csi is disabled (disable_hetzner_csi)

[UBaggeler]

This PR fixes https://github.com/kube-hetzner/terraform-hcloud-kube-hetzner/issues/1470 which was introduced with https://github.com/kube-hetzner/terraform-hcloud-kube-hetzner/pull/1417.

• If disable_hetzner_csi = false then csi_version will always be set (either from hetzner_csi_version or using the latest github release).
• If disable_hetzner_csi = true then csi_version will not be automatically be inferred from the latest github release. This is why rendering the templatefile fails, even though the file is not needed and ignored. This PR fixes rendering the template using coalesce. This way the file will be generated but is still not used since csi is disabled.

[olexiyb]

I came across the same issue I did next https://github.com/kube-hetzner/terraform-hcloud-kube-hetzner/commit/1d5a6721d157ac436aa1b2bb2f38d23ae9900f85

[UBaggeler]

I came across the same issue I did next 1d5a672

Yes, that's the other way to solve it.