.gitattributes: minor clean up

* Sorted the list - folders first, then files, alphabetic order.

.gitattributes

@@ -5,13 +5,13 @@
 # https://www.reddit.com/r/PHP/comments/2jzp6k/i_dont_need_your_tests_in_my_production
 # https://blog.madewithlove.be/post/gitattributes/
 #
-/.gitattributes   export-ignore
-/.gitignore       export-ignore
-/.cache/          export-ignore
-/.github/         export-ignore
-/.phpcs.xml.dist  export-ignore
-/phpunit.xml.dist export-ignore
-/tests/           export-ignore
+/.cache/         export-ignore
+/.github/        export-ignore
+/tests/          export-ignore
+.gitattributes   export-ignore
+.gitignore       export-ignore
+.phpcs.xml.dist  export-ignore
+phpunit.xml.dist export-ignore
 
 #
 # Auto detect text files and perform LF normalization