Remove 'tests'

Continuous of #3816.

Author: totoprayogo1916

user_guide_src/source/installation/installing_composer.rst

@@ -167,7 +167,7 @@ Structure
 
 Folders in your project after set up:
 
-- app, public, tests, writable (when using `--prefer-source`)
+- app, public, writable (when using `--prefer-source`)
 - vendor/codeigniter4/framework/system