fix(resource_github_actions_environment_secret): handle 404 on repo read

[scootafew]

Resolves #2407

Before the change?

Currently when running terraform destroy execution fails if the repository containing the environment secret was deleted outside terraform. The 404 is handled when querying the secret itself, but not in the prior request to get the repository id.

module.github.github_actions_environment_secret.secrets["MY_SECRET"]: Refreshing state... [id=repo:main:MY_SECRET]
╷
│ Error: GET https://api.github.com/repos/org/repo: 404 Not Found []
│ 
│   with module.github.github_actions_environment_secret.secrets["MY_SECRET"],
│   on ../core/github/main.tf line 134, in resource "github_actions_environment_secret" "secrets":
│  134: resource "github_actions_environment_secret" "secrets" {
│ 
╵

This is similar to #2115 & #1875

After the change?

If the repository no longer exists then the github_actions_environment_secret resource will be removed from the state (if the repo no longer exists then the secret cannot either).

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

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