Fix infection config extension in .gitattributes

Author: vudaltsov

.gitattributes

@@ -6,7 +6,7 @@
 /.gitignore              export-ignore
 /.php-cs-fixer.dist.php  export-ignore
 /composer.lock           export-ignore
-/infection.json.dist     export-ignore
+/infection.json5.dist    export-ignore
 /phpstan.dist.neon       export-ignore
 /phpunit.xml.dist        export-ignore
 /psalm.xml.dist          export-ignore