ci: update Terraform to 1.0.11

Changelogs:
- https://www.hashicorp.com/blog/announcing-hashicorp-terraform-1-0-general-availability
- https://www.terraform.io/language/upgrade-guides/1-0
- https://github.com/hashicorp/terraform/blob/v1.0/CHANGELOG.md

Part of #1720

[skip ci]

Author: php-coder

infra/terraform/.terraform-version

@@ -1 +1 @@
-0.15.5
+1.0.11

infra/terraform/versions.tf

@@ -1,5 +1,5 @@
 terraform {
-  required_version = ">= 0.15"
+  required_version = ">= 1.0"
 
   required_providers {
     digitalocean = {