fix(resource_github_release): Handle missing release in read

[arunsathiya]

Resolves #1864

---

Before the change?

• When a GitHub release is deleted manually (outside of Terraform state), resource_github_release doesn't handle that situation and throws an error. Example:

╷
│ Warning: Provider development overrides are in effect
│
│ The following provider development overrides are set in the CLI configuration:
│  - integrations/github in /Users/arun/go/bin
│
│ The behavior may therefore not match any released version of the provider and applying changes may cause the state to become incompatible with published
│ releases.
╵
github_repository.example: Refreshing state... [id=repo-terraform]
github_release.example: Refreshing state... [id=138562207]

Planning failed. Terraform encountered an error while generating this plan.

╷
│ Error: GET https://api.github.com/repos/arunsathiya/repo-terraform/releases/138562207: 404 Not Found []
│
│   with github_release.example,
│   on main.tf line 46, in resource "github_release" "example":
│   46: resource "github_release" "example" {
│
╵

After the change?

• resource_github_release now appropriately learns that the release is missing and informs Terraform state.

╷
│ Warning: Provider development overrides are in effect
│
│ The following provider development overrides are set in the CLI configuration:
│  - integrations/github in /Users/arun/go/bin
│
│ The behavior may therefore not match any released version of the provider and applying changes may cause the state to become incompatible with published
│ releases.
╵
tgithub_repository.example: Refreshing state... [id=repo-terraform]
 github_release.example: Refreshing state... [id=138566317]

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_release.example will be created
  + resource "github_release" "example" {
      + draft                  = false
      + etag                   = (known after apply)
      + generate_release_notes = false
      + id                     = (known after apply)
      + name                   = "example"
      + prerelease             = true
      + repository             = "repo-terraform"
      + tag_name               = "v1.0.3"
      + target_commitish       = "main"
    }

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

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

Saved the plan to: plan.tfplan

To perform exactly these actions, run the following command to apply:
    terraform apply "plan.tfplan"

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes
• No

---

[kfcampbell]

Thanks!