The ability to pull code represents only half of the Jenkins GitHub integration puzzle. The other half is to have GitHub trigger a Jenkins build when a developer pushes new code to the repository.
To implement a webhook, the GitHub hook trigger for GitScm polling must be enables on the Jenkins build job.
Namrataaswale
commented
1 year ago 
The ability to pull code represents only half of the Jenkins GitHub integration puzzle. The other half is to have GitHub trigger a Jenkins build when a developer pushes new code to the repository. To implement a webhook, the GitHub hook trigger for GitScm polling must be enables on the Jenkins build job.