vscode settings: update keybindings.json5 comments

This change replaces the reference to the deprecated "isTestCommand"
setting in keybindings.json5 with its replacement, "group": "test".
This makes keybindings.json5 match tasks.json5, which uses the new
syntax.

This also fixes a small typo.

Change-Id: Ie5a6cdb22610f27222105ff079e47dddd7160378
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2432138Reviewed-by: Chase Phillips <cmp@chromium.org>
Commit-Queue: Chase Phillips <cmp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813841}

tools/vscode/keybindings.json5

 // Place your key bindings in this file to overwrite the defaults
 [
-  // Run the task marked as "isTestCommand": true, see tasks.json.
+  // Run the task marked as "group": "test", see tasks.json.
   { "key": "ctrl+shift+t",       "command": "workbench.action.tasks.test" },
   // Jump to the previous change in the built-in diff tool.
   { "key": "ctrl+up",            "command": "workbench.action.compareEditor.previousChange" },
@@ -16,7 +16,7 @@
   // key binding from the C/C++ extension as I found it to be slow).
   { "key": "alt+o",              "command": "togglehs.toggleHS" },
   // Quickly run a task, see tasks.json. Since we named them 1-, 2- etc., it is
-  // suffucient to press the corresponding number.
+  // sufficient to press the corresponding number.
   { "key": "ctrl+r",             "command": "workbench.action.tasks.runTask",
                                     "when": "!inDebugMode" },
   // The following keybindings are useful on laptops with small keyboards such as