Invalid external-name on repository rulesets

[xunholy]

The resouerce tries to observe to calculate mutations, however because the external-name is wrong it can never import the resource and it thus fails.

The upstream terraform confirms this suspicion that it should not be the name string but rather the ID.

[Attributes Reference](https://registry.terraform.io/providers/integrations/github/latest/docs/resources/repository_ruleset#attributes-reference)
The following additional attributes are exported:

[etag](https://registry.terraform.io/providers/integrations/github/latest/docs/resources/repository_ruleset#etag-1) (String)

[node_id](https://registry.terraform.io/providers/integrations/github/latest/docs/resources/repository_ruleset#node_id-1) (String) GraphQL global node id for use with v4 API.

[ruleset_id](https://registry.terraform.io/providers/integrations/github/latest/docs/resources/repository_ruleset#ruleset_id-1) (Number) GitHub ID for the ruleset.

Error:

"message": "observe failed: failed to observe the resource: [{0 Unexpected ID format (\"REDACTED\"), expected numerical ID. strconv.ParseInt: parsing \"REDACTED\": invalid syntax  []}]",

[xunholy]

The issue is in the external_name.go logic. This could be also a problem for organisation rulesets but I have not confirmed.

// Can be imported using the following format: {{ repository }}:{{ ruleset id }}
"github_repository_ruleset": config.IdentifierFromProvider,