doc: fix wrong iam auth flag for sql_user

[eliecharra]

This PR was incorrect #10728

Flags are slightly inconsistent between MySQL and Postgres.

This fixes the flag for the Postgres example.

Release Note Template for Downstream PRs (will be copied)

See Write release notes for guidance.

cloudsql: fixed example in doc using wrong iam auth flag for PostgresQL in `google_sql_user`

[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.

@shuyama1, 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.

[wyardley]

I think I ran into this in the past, and was a pain to notice the difference, so thanks for fixing!

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 1 file changed, 2 insertions(+), 2 deletions(-))
google-beta provider: Diff ( 1 file changed, 2 insertions(+), 2 deletions(-))

[shuyama1]

Thanks for the fix!