Fix date parsing bug with grafana report updates

[mmandrus]

We received a customer escalation about updates to report dashboard.uids breaking configured timestamps. Now the time is parsed using the timestamp on the report.

I tested this locally by creating a report and then changing the report name, referenced dashboard, timestamps, and timezones, and verified all of the updates were processed correctly.

My terraform config for testing:

terraform {
  required_providers {
    grafana = {
      source  = "grafana/grafana"
      version = "~> 3.0"
    }
  }
}

provider "grafana" {
  url  = "http://localhost:3000"
  auth = "admin:admin"
}

resource "grafana_report" "test" {  
  name = "test-report"  
  formats = ["pdf"]  
  dashboards {  
    uid = "f8b7def7-22d3-4c03-9d91-8bc1c21aef9b"  
  }  
  recipients = ["[email protected]"]  
  schedule {  
    frequency = "hourly"  
    timezone = "Europe/Paris"  
    start_time = "2025-07-10T19:00:00"  
    end_time = "2025-07-17T19:00:00"  
  }  
}

[github-actions]

In order to lower resource usage and have a faster runtime, PRs will not run Cloud tests automatically.
To do so, a Grafana Labs employee must trigger the cloud acceptance tests workflow manually.