fix: correct space id support for creating variables

[benPearce1]

fixes #771

before:

Plan: 1 to add, 0 to change, 0 to destroy.
octopusdeploy_variable.string: Creating...
╷
│ Error: create variable failed
│ 
│   with octopusdeploy_variable.string,
│   on main.tf line 31, in resource "octopusdeploy_variable" "string":
│   31: resource "octopusdeploy_variable" "string" {
│ 
│ Octopus API error: Resource is not found or it doesn't exist in the current space context. Please contact your administrator for more information. [] 

after:

Plan: 1 to add, 0 to change, 0 to destroy.
octopusdeploy_variable.string: Creating...
octopusdeploy_variable.string: Creation complete after 0s [id=9e0fcce6-1fe3-4fe3-a8ab-7455247be95d]

Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

[IsaacCalligeros95]

LGTM

[hnrkndrssn]

LGTM