feat(gha): unify GHA - renovate, megalinter, markdown, and others

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[github-actions]

terraform init Failed

Initializing the backend...

Initializing provider plugins...
- Finding latest version of hashicorp/openstack...
- Finding latest version of hashicorp/null...
- Installing hashicorp/null v3.2.2...
- Installed hashicorp/null v3.2.2 (signed by HashiCorp)
╷
│ Warning: Quoted references are deprecated
│ 
│   on main.tf line 100, in resource "null_resource" "vms":
│  100:   depends_on = ["openstack_compute_floatingip_associate_v2.floatingip-associate"]
│ 
│ In this context, references are expected literally rather than in quotes.
│ Terraform 0.11 and earlier required quotes, but quoted references are now
│ deprecated and will be removed in a future version of Terraform. Remove the
│ quotes surrounding this reference to silence this warning.
│ 
│ (and one more similar warning elsewhere)
╵

╷
│ Error: Failed to query available provider packages
│ 
│ Could not retrieve the list of available versions for provider
│ hashicorp/openstack: provider registry registry.terraform.io does not have
│ a provider named registry.terraform.io/hashicorp/openstack
│ 
│ Did you intend to use terraform-provider-openstack/openstack? If so, you
│ must specify that source address in each module which requires that
│ provider. To see which modules are currently depending on
│ hashicorp/openstack, run the following command:
│     terraform providers
╵

Workflow: terraform, Action: __hashicorp_terraform-github-actions_2, Working Directory: terraform/openstack