esm: fix import assertion warning

Refs: nodejs#46901 (comment)

Author: aduh95

lib/internal/modules/esm/assert.js

@@ -61,8 +61,8 @@ function validateAssertions(url, format,
   if (!alreadyWarned && ObjectKeys(importAssertions).length !== 0) {
     alreadyWarned = true;
     process.emitWarning(
-      'Import assertions are not a stable feature of the JavaScript language, ' +
-      'avoid relying on their current behavior and syntax as those might change ' +
+      'Import assertions are not a stable feature of the JavaScript language. ' +
+      'Avoid relying on their current behavior and syntax as those might change ' +
       'in a future version of Node.js.',
       'ExperimentalWarning',
     );