Fix end positions for at-rule-no-unknown

[ybiquitous]

Which issue, if any, is this issue related to?

Part of #5694

Is there anything in the PR that needs further explanation?

I think the range should be at an at-rule name, not an at-rule block. E.g.,

    @unknown (max-width: 960px) {}
/** ↑------↑ */

[jeddy3]

LGTM, thank you!

Shall we classify these as fixes or additions? e.g. "Fixed: at-rule-no-unknown end positions" or "Added: at-rule-no-unknown range support"

[ybiquitous]

Shall we classify these as fixes or additions? e.g. "Fixed: at-rule-no-unknown end positions" or "Added: at-rule-no-unknown range support"

I think this change belongs to fixes because end positions have been supported.

Here is an example of using the latest Stylelint version:

$ echo '@abc {}' > a.css

$ echo '{"rules":{"at-rule-no-unknown":true}}' > .stylelintrc.json

$ npx stylelint a.css -f json | jq .
[
  {
    "source": "/private/tmp/foo/a.css",
    "deprecations": [],
    "invalidOptionWarnings": [],
    "parseErrors": [],
    "errored": true,
    "warnings": [
      {
        "line": 1,
        "column": 1,
        "endLine": 1,
        "endColumn": 8,
        "rule": "at-rule-no-unknown",
        "severity": "error",
        "text": "Unexpected unknown at-rule \"@abc\" (at-rule-no-unknown)"
      }
    ]
  }
]

"endColumn": 8 is output now, but "endColumn": 5 will be output by this pull request.

[jeddy3]

SGTM. Feel free to merge.

[ybiquitous]

Changelog entry added:

• Fixed: at-rule-no-unknown end positions (#6026).