Just correcting a small typo and changing key. Fixes #20508

Why:

Fixing a small typo in the docs and changing subkey in paste-gpg-key-id.md to match copy-gpg-key-id.md 📝

What's being changed (if available, include any code snippets, screenshots, or gifs):

- Once your PR is merged, your contributions will be publicly visible on the [GitHubs docs](https://docs.github.com/en). 
+ Once your PR is merged, your contributions will be publicly visible on the [GitHub docs](https://docs.github.com/en). 

- Alternatively, when setting a subkey include the `!` suffix. In this example, the GPG subkey ID is `4BB6D45482678BE3`:
+ Alternatively, when setting a subkey include the `!` suffix. In this example, the GPG subkey ID is `42B317FD4BA89E7A`:
```shell
- $ git config --global user.signingkey <em>4BB6D45482678BE3</em>!
+ $ git config --global user.signingkey <em>42B317FD4BA89E7A</em>!

Check off the following:

• I have reviewed my changes in staging (look for the "Automatically generated comment" and click the links in the "Preview" column to view your latest changes).
• For content changes, I have completed the self-review checklist.

Writer impact (This section is for GitHub staff members only):

• This pull request impacts the contribution experience
  • I have added the 'writer impact' label
  • I have added a description and/or a video demo of the changes below (e.g. a "before and after video")