Variable block should not show completion items for the target block

[rcjsuen]

The inherits and network attributes should not show anything since we are actually inside a variable block.

variable "var" {
  inherits = [""]
  network = ""
}

target "base" {
}

{
    "textDocument": {
        "uri": "file:///tmp/docker-bake.hcl"
    },
    "position": {
        "line": 1,
        "character": 15
    },
    "context": {
        "triggerKind": 1
    }
}

{
    "isIncomplete": false,
    "items": [
        {
            "label": "base"
        }
    ]
}

{
    "textDocument": {
        "uri": "file:///tmp/docker-bake.hcl"
    },
    "position": {
        "line": 2,
        "character": 13
    },
    "context": {
        "triggerKind": 1
    }
}

{
    "isIncomplete": false,
    "items": [
        {
            "label": "default"
        },
        {
            "label": "host"
        },
        {
            "label": "none"
        }
    ]
}