Bug 1706301 - Fix inert-node-is-unselectable.tentative.html. r=masayuki

Seems legit to select the whitespace around the inert node.

Differential Revision: https://phabricator.services.mozilla.com/D112718

testing/web-platform/meta/inert/inert-node-is-unselectable.tentative.html.ini

@@ -1,4 +0,0 @@
-[inert-node-is-unselectable.tentative.html]
-  [Inert nodes cannot be selected.]
-    expected: FAIL
-

testing/web-platform/tests/inert/inert-node-is-unselectable.tentative.html

@@ -13,7 +13,7 @@
 <script>
 test(function() {
     document.execCommand('SelectAll');
-    assert_equals(window.getSelection().toString(), "I'm selectable.");
+    assert_equals(window.getSelection().toString().trim(), "I'm selectable.");
 }, "Inert nodes cannot be selected.");
 </script>
 </body>