fix scheduler_job_http example

[modular-magician]

Minor fix: repair a syntax error in the Cloud Scheduler HTTP target example, introduced in #4247.

I was able to generate the terraform provider code and manually verify that the newly generated doc is correct, but I'm not set up for go development so wasn't able to run the tests. As far as I can tell they didn't catch the error in the first place so I'm not too worried about it, but let me know if you need me to work through it.

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

scheduler: Fixed syntax error in the Cloud Scheduler HTTP target example.

Derived from GoogleCloudPlatform/magic-modules#4280

[ghost]

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