[BUG] github_repository resource errors with squash_merge/merge commit message/title

[aliculPix4D]

Short summary:
resource_github_repository tries to update the fields squash_merge_commit_message/squash_merge_commit_title
eventhough the allow_squash_merge is set to false. The terraform state is correctly updated with default values (i.e

terraform-provider-github/github/resource_github_repository.go

Line 186 in 42ebbe0

Default: "COMMIT_MESSAGES",

) but the Github API call can't be done because the allow_squash_merge is set to false before and the endpoints to configure squash_merge_commit_message/squash_merge_commit_title are not available anymore.

Note that the same issue will occur with both: squash_merge_commit_message/squash_merge_commit_title and merge_commit_message/merge_commit_title pairs.

Minimal example to reproduce the bug:

Step 1: apply the following configuraion.

terraform {
  required_version = "1.4.6"

  required_providers {
    github = {
      source  = "integrations/github"
      version = "5.25.1"
    }
  }
}

provider "github" {
  token = var.github_token
  owner = "yourOrganization"
}

variable "github_token" {
  type = string
}

resource "github_repository" "repo" {
  name        = "test-repository-name"
  allow_squash_merge = true
  squash_merge_commit_message = "PR_BODY"
  squash_merge_commit_title   = "PR_TITLE"
}

Step 2: change your configuration to :

resource "github_repository" "repo" {
  name        = "test-repository-name"
  allow_squash_merge = false
}

Step 3: and run terraform apply

Terraform will perform the following actions:

  # github_repository.repo will be updated in-place
  ~ resource "github_repository" "repo" {
      ~ allow_squash_merge          = true -> false
        id                          = "test-repository-name"
        name                    = "test-repository-name"
      ~ squash_merge_commit_message = "PR_BODY" -> "COMMIT_MESSAGES"
      ~ squash_merge_commit_title   = "PR_TITLE" -> "COMMIT_OR_PR_TITLE"
        # (29 unchanged attributes hidden)
    }

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

will result in:

github_repository.repo: Modifying... [id=test-repository-name]
╷
│ Error: PATCH https://api.github.com/repos/yourOrganization/test-repository-name: 422 Validation Failed [{Resource:Repository Field:merge_commit_allowed Code:invalid Message:Sorry, you need to allow the squash merge strategy in order to set the default squash commit message title or message. (no_squash_merge_strategy)}]
│ 
│   with github_repository.repo,
│   on main.tf line 21, in resource "github_repository" "repo":
│   21: resource "github_repository" "repo" {
│ 
╵

Step 4: but the next terraform plan/apply will always be empty.
No changes. Your infrastructure matches the configuration.

Possibly connected to: #1295