Exclude the tests folder from phpcs checker

phpcs.xml

@@ -7,6 +7,7 @@
     <exclude-pattern>node_modules/*</exclude-pattern>
     <exclude-pattern>vendor/*</exclude-pattern>
     <exclude-pattern>lib/*</exclude-pattern>
+    <exclude-pattern>tests/*</exclude-pattern>
     <rule ref="WordPress-Core">
         <exclude name="Squiz.Commenting.FileComment.SpacingAfterComment" />
         <exclude name="Generic.Files.LowercasedFilename" />