fix: typo in step 2

[j-brisard]

Summary

Fix a grammatical error in the task list description section.

Changes

Removes redundant "is" from the sentence describing task lists.

Before: "A task list is extends the unordered list to use check boxes."
After: "A task list extends the unordered list to use check boxes."

Closes:

Task list

• For workflow changes, I have verified the Actions workflows function as expected.
• For content changes, I have reviewed the style guide.