Update isolates.md

[Coloud1]

Updated the link to Concurrency and isolates from flutter.dev to docs.flutter.dev. Updated link leading to dart api documentation about Isolate.run

Fixes #6051

---

• I’ve reviewed the contributor guide and applied the relevant portions to this PR.
• This PR doesn't contain automatically generated corrections or text (Grammarly, LLMs, and similar).
• This PR follows the Google Developer Documentation Style Guidelines — for example, it doesn't use i.e. or e.g., and it avoids I and we (first person).
• This PR uses semantic line breaks of 80 characters or fewer.

Contribution guidelines:

• See our contributor guide for general expectations for PRs.
• Larger or significant changes should be discussed in an issue before creating a PR.
• Code changes should generally follow the Dart style guide and use dart format.
• Updates to code excerpts indicated by <?code-excerpt need to be updated in their source .dart file as well.

[sfshaza2]

lgtm

[sfshaza2]

Wow, that "/" comment was a typo. I never knew that it could close a PR!

[sfshaza2]

/gcbrun

[dart-github-bot]

Visit the preview URL for this PR (updated for commit f08800c):

https://dart-dev--pr6052-patch-3-mnappl7f.web.app

[Coloud1]

Wow, that "/" comment was a typo. I never knew that it could close a PR!

But now we both know about it (:

[parlough]

Thanks for catching and fixing these links!

[parlough]

Thanks for catching and fixing these links!