Build/Test Tools: Add a missing word to the CONTRIBUTING.md file.

Follow up to [50417].

Props kraftbj.
See #33043.

git-svn-id: https://develop.svn.wordpress.org/trunk@50421 602fd350-edb4-49c9-b593-d223f7449a82

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 
 For the in-depth documentation, please visit the [Contributor Handbook](https://make.wordpress.org/core/handbook/contribute/).
 
-**Core WordPress Development does not occur on GitHub; however, pull requests are accepted as long there is a corresponding [Trac](https://core.trac.wordpress.org) ticket.**
+**Core WordPress Development does not occur on GitHub; however, pull requests are accepted as long as there is a corresponding [Trac](https://core.trac.wordpress.org) ticket.**
 
 For WordPress Block Editor development, please see the [Gutenberg GitHub repository](https://github.com/wordpress/gutenberg/).