git: access-control-list cannot be updated, and the user receives an erroneous "requires replacement" warning if they attempt to do so #1633

Description

Please add a clear and concise description of what the bug is.

Steps to reproduce

1. Define a git instance resource

resource "stackit_git" "instance" {
  project_id = var.stackit_project_id
  name       = "cannot-update-acls"
  flavor     = "git-10"
  acl        = [ "0.0.0.0/0" ]
}

2. Create the instance (apply)

terraform apply

3. Modify the ACL

resource "stackit_git" "instance" {
  project_id = var.stackit_project_id
  name       = "cannot-update-acls"
  flavor     = "git-10"
  acl        = [ "127.0.0.1/32" ]
}

4. Update the instance (apply)

terraform apply

5. Note the "forces replacement" warning

6. Additionally, if the user proceeds with the apply, nothing actually takes place. The instance is not updated or deleted. Instead an error message informs the user that updating git instances is not supported.

w. First apply (create) a git instance with a terraform block such as

resource "stackit_git" "git_10" {
  project_id = var.stackit_project_id
  name       = "cannot-update-acls"
  flavor     = "git-10"
  acl        = [ "0.0.0.0/0" ]
}

Actual behavior

1. When the user attempts to update a Git instance access-control-list, the provider warns the user that this will force a replacement of the git instance (1 to destory, 1 to create)
2. If the user proceeds with the apply, the provider logs an error stating that the update flow is not supported.

Expected behavior

1. A user should be able to change the access-control-list without this being flagged as a replacement.
2. The user should be able to update git resources.

Environment

• OS: darwin_arm64
• Terraform version (see terraform --version): v1.15.8
• Version of the STACKIT Terraform provider: v0.106.0

Additional information

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