fix: support paring warnings without -no-color

[suzuki-shunsuke]

Follow up #903

Example

main.tf

resource "github_repository" "tfcmt" {
  name           = "tfcmt"
  default_branch = "main" # Deprecated field
}

terraform plan

Terraform used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
  + create

Terraform will perform the following actions:

  # github_repository.tfcmt will be created
  + resource "github_repository" "tfcmt" {
      + allow_auto_merge            = false
      + allow_merge_commit          = true
      + allow_rebase_merge          = true
      + allow_squash_merge          = true
      + archived                    = false
      + default_branch              = "main"
      + delete_branch_on_merge      = false
      + etag                        = (known after apply)
      + full_name                   = (known after apply)
      + git_clone_url               = (known after apply)
      + html_url                    = (known after apply)
      + http_clone_url              = (known after apply)
      + id                          = (known after apply)
      + merge_commit_message        = "PR_TITLE"
      + merge_commit_title          = "MERGE_MESSAGE"
      + name                        = "tfcmt"
      + node_id                     = (known after apply)
      + primary_language            = (known after apply)
      + private                     = (known after apply)
      + repo_id                     = (known after apply)
      + squash_merge_commit_message = "COMMIT_MESSAGES"
      + squash_merge_commit_title   = "COMMIT_OR_PR_TITLE"
      + ssh_clone_url               = (known after apply)
      + svn_url                     = (known after apply)
      + topics                      = (known after apply)
      + visibility                  = (known after apply)
    }

Plan: 1 to add, 0 to change, 0 to destroy.

Changes to Outputs:
  + foo = "foo"
╷
│ Warning: "default_branch": [DEPRECATED] Use the github_branch_default resource instead
│ 
│   with github_repository.tfcmt,
│   on main.tf line 10, in resource "github_repository" "tfcmt":
│   10: resource "github_repository" "tfcmt" {
│ 
│ (and one more similar warning elsewhere)
╵

─────────────────────────────────────────────────────────────────────────────

Note: You didn't use the -out option to save this plan, so Terraform can't
guarantee to take exactly these actions if you run "terraform apply" now.