.gitattributes: update for PHPUnit config

Follow up on #6

Author: jrfnl

.gitattributes

@@ -5,11 +5,12 @@
 # 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
-/.github       export-ignore
-/c             export-ignore
-/tests         export-ignore
+.gitattributes   export-ignore
+.gitignore       export-ignore
+phpunit.xml.dist export-ignore
+/.github         export-ignore
+/c               export-ignore
+/tests           export-ignore
 
 #
 # Auto detect text files and perform LF normalization