.gitattributes: minor clean up

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

.gitattributes

@@ -5,16 +5,16 @@
 # 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
-/.markdownlint-cli2.yaml export-ignore
-/.phpcs.xml.dist export-ignore
-/.remarkignore export-ignore
-/.remarkrc 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
+.markdownlint-cli2.yaml export-ignore
+.phpcs.xml.dist         export-ignore
+.remarkignore           export-ignore
+.remarkrc               export-ignore
+phpunit.xml.dist        export-ignore
 
 #
 # Auto detect text files and perform LF normalization