Upgrade terraform test dependencies.

[markmandel]

What type of PR is this?

Uncomment only one /kind <> line, press enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking
/kind bug

/kind cleanup

/kind documentation
/kind feature
/kind hotfix

What this PR does / Why we need it:

Fix for security alert:
https://github.com/googleforgames/agones/security/dependabot/test/terraform/go.sum/gopkg.in%2Fyaml.v2/open

This is a low risk alert, since it's on a rarely used test hardness, but good to provide an update and remove the alert by updating the core libraries.

Which issue(s) this PR fixes:

N/A

Special notes for your reviewer:

N/A

[markmandel]

I thought I was marking the alert as "work in progress", but apparently I dismissed it 🤦🏻

New link:
https://github.com/googleforgames/agones/security/dependabot/test/terraform/go.sum/gopkg.in%2Fyaml.v2/closed

[agones-bot]

Build Succeeded 👏

Build Id: c6cd545a-852d-407e-9963-84aa7ec4ef76

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.20.0-a36734f
• image: gcr.io/agones-images/agones-ping:1.20.0-a36734f
• Linux C++ SDK (build): agonessdk-1.20.0-a36734f-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.20.0-a36734f.zip

A preview of the website (the last 30 builds are retained):

• https://a36734f-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2425/head:pr_2425 && git checkout pr_2425
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.20.0-a36734f

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: markmandel, roberthbailey

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• OWNERS [markmandel,roberthbailey]

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[roberthbailey]

Merging during the feature freeze since this only affects the terraform test code and is a security fix.