Bug: Leading underscores in variable are not allowed

[dhilgarth]

resource "bitbucket_deployment_variable" "db_database" {
  workspace  = var.bitbucket_workspace
  repository = "neuroflash_api"
  deployment = "{XXX}"
  key        = "___DB_DATABASE"
  value      = azurerm_mysql_flexible_database.db.name
  secured    = false
}

This leads to variable name must consist of only ASCII letters, numbers, underscores & not begin with a number (a-z, 0-9, _). However, leading underscores are in fact allowed