Revert "minor #54653 Auto-close PRs on subtree-splits (nicolas-grekas)"

This reverts commit 2c9352dd91ebaf37b8a3e3c26fd8e1306df2fb73, reversing
changes made to 18c3e87f1512be2cc50e90235b144b13bc347258.

Author: fabpot

.gitattributes

@@ -1,3 +1,4 @@
 /Tests export-ignore
 /phpunit.xml.dist export-ignore
-/.git* export-ignore
+/.gitattributes export-ignore
+/.gitignore export-ignore