Fixes older TFE, tfe_workspace_settings always unsets execution_mode

[brandonc]

Description

I made a mistake with tfe_workspace_settings compatibility. The "unknownIfExecutionModeUnset" plan modifier was supposed to actually check for unsetting before changing the planned value of execution_mode when it had no overwrites to consult.

Tested on TFC and TFE v202308-1

Remember to:

• Update the Change Log
• Update the Documentation

Testing plan

1. Use this config. Run terraform apply twice. It works fine on the last couple of TFE releases (this is why there are no acceptance tests) but on v202308-1 the second plan fails

Sample Config

terraform {
  required_providers {
    tfe = {
      source = "hashicorp/tfe"
      version = "0.51.0"
    }
  }
}

provider "tfe" {
}

resource tfe_organization "org" {
  name = "test-IPL5516-tfe"
  email = "[email protected]"
}

// 1
resource "tfe_agent_pool" "pool" {
  name         = "pool"
  organization = tfe_organization.org.id
  organization_scoped = false
}

// 2
resource "tfe_workspace" "test" {
  name         = "test-123360"
  organization = tfe_organization.org.id
}

// 3
resource "tfe_agent_pool_allowed_workspaces" "pool" {
  agent_pool_id = tfe_agent_pool.pool.id
  allowed_workspace_ids = [for key, value in tfe_workspace.test.*.id : value]
}

// 4
resource "tfe_workspace_settings" "test-settings" {
  execution_mode = "agent"
  agent_pool_id = tfe_agent_pool_allowed_workspaces.pool.agent_pool_id
  workspace_id   = tfe_workspace.test.id
}

External links

Include any links here that might be helpful for people reviewing your PR. If there are none, feel free to delete this section.

• go-tfe documentation
• API documentation
• Related PR