Fix typo on word 'Certificate' for map description

[naheedtayab]

Release Note Template for Downstream PRs (will be copied)

See Write release notes for guidance.

certificatemanager: Fixed typo for map entry description on word 'Certificate'

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[github-actions]

Hello! I am a robot. Tests will require approval from a repository maintainer to run.

Googlers: For automatic test runs see go/terraform-auto-test-runs.

@NickElliot, a repository maintainer, has been assigned to review your changes. If you have not received review feedback within 2 business days, please leave a comment on this PR asking them to take a look.

You can help make sure that review is quick by doing a self-review and by running impacted tests locally.

[github-actions]

@NickElliot This PR has been waiting for review for 3 weekdays. Please take a look! Use the label disable-review-reminders to disable these notifications.

[github-actions]

@GoogleCloudPlatform/terraform-team @NickElliot This PR has been waiting for review for 1 week. Please take a look! Use the label disable-review-reminders to disable these notifications.