Add .gitattributes (#53)

* Add `.gitattributes`

* Reverting changes in `.github/workflows/downgraded_release.yaml`, although I believe having this step is unnecessary

Author: kubawerlos

.gitattributes

@@ -0,0 +1,7 @@
+/.* export-ignore
+/build/ export-ignore
+/tests/ export-ignore
+/ecs.php export-ignore
+/phpstan.neon export-ignore
+/phpunit.xml export-ignore
+/rector.php export-ignore