fix: remove -auto-approve from apply jobs with upstream plans

The -auto-approve option is ignored when a plan is present, as explained by the
[documentation](https://developer.hashicorp.com/terraform/cli/commands/apply#auto-approve). When
this option is present for a Terraform Enterprise/Cloud setup, the apply command is never run, and
the CLI job times out. Considering the option is ignored (also by [older
versions](https://developer.hashicorp.com/terraform/cli/v1.1.x/commands/apply#auto-approve)),
removing the option entirely seems to be the best solution.