Fix checkstyle test

Author: jimhester

tests/testthat/checkstyle.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<checkstyle version="lintr-3.0.0">
+<checkstyle version="lintr-3.0.0.9000">
   <file name="test_file">
     <error line="1" column="2" severity="error" message="foo"/>
     <error line="2" column="1" severity="info" message="bar"/>