Incorrectly removing resource state from state file on http error

[michaeldu93]

Hi, I have raised a PR here to address this issue, can you have a look please?
#67

Description

• HTTP error other than 404 will cause terraform to remove the resource state from the state file after this change has been merged
  • 404 handling for deleted resources #41
• The status code for 404, connection reset, connection timeout are all 0
  • For Example

2025-02-17T15:15:47.984Z [WARN]  provider.terraform-provider-synthetics: Synthetics API error. Retrying. Attempt 122510 Get "https://api.eu0.signalfx.com/v2/synthetics/tests/browser/22510": context deadline exceeded (Client.Timeout exceeded while awaiting headers) 0 0: timestamp=2025-02-17T15:15:47.984Z

• This means that when the request times out or the connection reset etc, the state will be removed and it will try and create it with the resource already there, ending up with
  Error: Status Code: 422 Unprocessable Entity
Response: {"message":"Could not create Browser Test","details":{"name":["has already been taken"]}}
• The error message of a 404 is also not matching correctly, it's currently using an absolute match with Status Code: 404 Not Found but the error message is actually (on two lines)
  Status Code: 404 Not Found
Response: {"message":"Record not found"}
• For Example

2025-02-17T14:42:54.186Z [WARN]  provider.terraform-provider-synthetics: Synthetics API error. Retrying. 22455 Status Code: 404 Not Found
Response: {"message":"Record not found"} 0 0: timestamp=2025-02-17T14:42:54.186Z