Update testify package in gomod

[akremsa]

What type of PR is this?

/kind cleanup

What this PR does / Why we need it:
I need a new functionality provided by a recent version of testify, that is why I decided to perform this update.

[agones-bot]

Build Succeeded 👏

Build Id: 78714b40-4573-4538-8657-b5ff9aa7241d

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

• image: gcr.io/agones-images/agones-controller:1.6.0-3f884f0
• image: gcr.io/agones-images/agones-sdk:1.6.0-3f884f0
• image: gcr.io/agones-images/agones-ping:1.6.0-3f884f0
• Linux C++ SDK (build): agonessdk-1.6.0-3f884f0-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.6.0-3f884f0.zip

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

• https://3f884f0-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/1492/head:pr_1492 && git checkout pr_1492
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.6.0-3f884f0

[aLekSer]

Please use go 1.13.5 as in make shell. 34 Files is too many. I got 8:

 git diff --name-only  | wc -l
       8

Thanks, deleting Prometheus testutil.go seems to be my miss, when I updated opencensus to a new version and then test separately.

[agones-bot]

Build Succeeded 👏

Build Id: 0d71def0-d588-4adf-a48a-940f1b816c31

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

• image: gcr.io/agones-images/agones-controller:1.6.0-94c244e
• image: gcr.io/agones-images/agones-sdk:1.6.0-94c244e
• image: gcr.io/agones-images/agones-ping:1.6.0-94c244e
• Linux C++ SDK (build): agonessdk-1.6.0-94c244e-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.6.0-94c244e.zip

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

• https://94c244e-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/1492/head:pr_1492 && git checkout pr_1492
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.6.0-94c244e

[aLekSer]

Tested this update locally. Same results.

[google-oss-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: akremsa, aLekSer
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