Fix counting of error deletion in linter

Related feedback:
- https://github.com/uBlockOrigin/uAssets/discussions/17538#discussioncomment-5628053

src/js/codemirror/ubo-static-filtering.js

@@ -840,6 +840,7 @@ CodeMirror.registerHelper('fold', 'ubo-static-filtering', (( ) => {
             if ( marker === null ) { return; }
             if ( marker.dataset.lint === 'error' ) {
                 errorCount -= 1;
+                marker.dataset.lint = 'void';
             }
         });
     };