docs: fix unclosed info admonition in authorizing-the-slack-cli (#604)

The `:::info` block about `--skip-update` / `SLACK_SKIP_UPDATE` being
ignored by `slack upgrade` was missing the closing `]` on its title.
The unclosed title bracket caused the MDX renderer to mangle later
content on the page, surfacing a stray `authorize-cli}` in the preview.

Co-authored-by: Claude <svc-devxp-claude@slack-corp.com>

Author: zimeg

docs/guides/authorizing-the-slack-cli.md

@@ -65,7 +65,7 @@ Update notifications can be disabled using a command-line flag or an environment
 
 When the CLI runs in a non-interactive environment, such as inside a CI/CD pipeline or when the output is piped, the update check runs without the auto-update confirmation prompt. The notification text may still appear in command output, however. You can suppress the check entirely with the `--skip-update` flag or `SLACK_SKIP_UPDATE` environment variable to keep the automation output clean.
 
-:::info[The `--skip-update` flag and the `SLACK_SKIP_UPDATE` environment variable are intentionally ignored when running the `slack upgrade` command directly, since that command's purpose is to check for updates.
+:::info[The `--skip-update` flag and the `SLACK_SKIP_UPDATE` environment variable are intentionally ignored when running the `slack upgrade` command directly, since that command's purpose is to check for updates.]
 :::
 
 ## CI/CD authorization {#ci-cd}