Bump concurrent-ruby from 1.2.2 to 1.3.7 in /docs - #2

Process completed with exit code 2.

src/Util/RegexHelper.php:132:25: ArgumentTypeCoercion: Argument 1 of preg_match_all expects non-empty-string, but parent type string provided (see https://psalm.dev/193)

src/Util/RegexHelper.php:109:27: ArgumentTypeCoercion: Argument 1 of preg_match expects non-empty-string, but parent type string provided (see https://psalm.dev/193)

src/Parser/InlineParserEngine.php:147:35: ArgumentTypeCoercion: Argument 1 of preg_match_all expects non-empty-string, but parent type string provided (see https://psalm.dev/193)

src/Parser/Cursor.php:401:27: ArgumentTypeCoercion: Argument 1 of preg_match expects non-empty-string, but parent type string provided (see https://psalm.dev/193)

src/Extension/ExternalLink/ExternalLinkProcessor.php:104:33: ArgumentTypeCoercion: Argument 1 of preg_match expects non-empty-string, but parent type string provided (see https://psalm.dev/193)

src/Extension/Embed/DomainFilteringAdapter.php:37:32: ArgumentTypeCoercion: Argument 1 of preg_match expects non-empty-string, but parent type string provided (see https://psalm.dev/193)

src/Extension/CommonMark/Parser/Block/ListBlockStartParser.php:73:25: ArgumentTypeCoercion: Argument 1 of preg_match expects non-empty-string, but parent type string provided (see https://psalm.dev/193)

src/Extension/CommonMark/Parser/Block/HtmlBlockParser.php:71:29: ArgumentTypeCoercion: Argument 1 of preg_match expects non-empty-string, but parent type string provided (see https://psalm.dev/193)

src/Extension/Autolink/UrlAutolinkParser.php:92:27: ArgumentTypeCoercion: Argument 1 of preg_match expects non-empty-string, but parent type string provided (see https://psalm.dev/193)

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/