added github handle variable for Bitian Zhang to civic-tech-jobs.md

[Brayheart]

Fixes #6123

What changes did you make?

• Added " github-handle:" to line 85 in _projects/civic-tech-jobs.md

Why did you make the changes (we will use this info to test)?

• this variable will replace the existing github and picture variables, reducing redundancy in the project data

Creating new var in md file, no visual changes to the website.

[github-actions]

Want to review this pull request? Take a look at this documentation for a step by step guide!

From your project repository, check out a new branch and test the changes.

git checkout -b Brayheart-github-handle-for-Bitian-Zhang-in-civic-tech-jobs.md-#6123 gh-pages
git pull https://github.com/Brayheart/Hack_for_LA_website.git github-handle-for-Bitian-Zhang-in-civic-tech-jobs.md-#6123

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Note that CONTRIBUTING.md cannot previewed locally; rather it should be previewed at this URL:

https://github.com/Brayheart/website/blob/github-handle-for-Bitian-Zhang-in-civic-tech-jobs.md-#6123/CONTRIBUTING.md  

[heejung-hong]

Good work!

• The branches are correct and the issue is linked.
• The correct file was changed with the correct information.
• I have inspected and confirmed the changes in developer mode on Chrome (desktop, tablet, and mobile view), Firefox, and Safari browser.

[jphamtv]

Hey @Brayheart - Thanks for working on this issue. Your summary of changes is clear and your code change is clean and accurate. Great work!