Fix panic in intergration resource update

[cderici]

Description

This is a quick run-by fix for something I bumped into when I was working on #235. Looks like the type of the applications in integration resource's Update is set to be an Attribute instead of a Block like in the Schema.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Environment

• Juju controller version: 2.9

• Terraform version: 1.5

QA steps

Any plan that updates an integration would hit that. I'll add the plan that I was using when I bumped into this one.

Apply the plan below, let it settle, then uncomment the wordpresstwo and change the app name in the integration.

resource "juju_model" "development" {
  name = "development"
}

resource "juju_application" "wordpress" {
  name = "wordpress"

  model = juju_model.development.name

  charm {
    name = "wordpress"
  }

  units = 3
}


/*
resource "juju_application" "wordpresstwo" {
  name = "wordpresstwo"

  model = juju_model.development.name

  charm {
    name = "wordpress"
  }

  units = 3
}
*/


resource "juju_application" "percona-cluster" {
  name = "percona-cluster"

  model = juju_model.development.name

  charm {
    name = "percona-cluster"
  }

  units = 3
}

resource "juju_integration" "wp_to_percona" {
  model = juju_model.development.name

  application {
    name     = juju_application.wordpress.name # <---------- change this to wordpresstwo
    endpoint = "db"
  }

  application {
    name     = juju_application.percona-cluster.name
    endpoint = "db"
  }
}

[hmlanigan]

Please update the commit message to describe why and how this fixes the panic.

We need an AT which tests Update.