Update URL for GitHubFlow original blog post

The URL for the GitHubFlow's original blog post resource has been corrected. The previous link was not functioning properly and provided an incorrect address. The new link ensures users are directed to the correct resource page.

Author: arturcic

docs/input/docs/learn/branching-strategies/githubflow/index.md

@@ -24,6 +24,6 @@ GitHub Flow allows and encourages [continuous delivery](/docs/reference/modes/co
 ## Resources
 
 *   [GitHubFlow guide by GitHub](https://docs.github.com/en/get-started/quickstart/github-flow#introduction)
-*   [GitHubFlow original blog post](https://scottchacon.com/2011/08/31/github-flow.html)
+*   [GitHubFlow original blog post](https://scottchacon.com/2011/08/31/github-flow)
 *   [Phil Haack's (haacked) GitHubFlow aliases](https://haacked.com/archive/2014/07/28/github-flow-aliases/)
 *   [GitHubFlow vs GitFlow](https://lucamezzalira.com/2014/03/10/git-flow-vs-github-flow/)