chore: exclude release please config files from git export

Author: carlalexander

.gitattributes

@@ -4,7 +4,9 @@
 .gitattributes export-ignore
 .gitignore export-ignore
 .php-cs-fixer.dist.php export-ignore
+.release-please-manifest.json export-ignore
 grumphp.yml export-ignore
 phpmd.xml export-ignore
 phpstan.neon export-ignore
 phpunit.xml.dist export-ignore
+release-please-config.json export-ignore