Fix build command: build-agones-sdk-image

[govargo]

What type of PR is this?

/kind bug

What this PR does / Why we need it:

I found that agones-sdk image build command failed when I tried to test make run-sdk-conformance-test.
The command has changed, but it seems to have leaked in #2521.

Before this PR

% make ensure-agones-sdk-image
/Library/Developer/CommandLineTools/usr/bin/make ensure-image IMAGE_TAG=gcr.io/agones-images/agones-sdk:1.24.0-11f7c21-linux-amd64 BUILD_TARGET=build-agones-sdk-server-image
Could not find gcr.io/agones-images/agones-sdk:1.24.0-11f7c21-linux-amd64 image. Building...
make[2]: *** No rule to make target `build-agones-sdk-server-image'.  Stop.
make[1]: *** [ensure-image] Error 2
make: *** [ensure-agones-sdk-image] Error 2

BUILD_TARGET=build-agones-sdk-server-image is defined, but it doesn't exist.
The correct one is build-agones-sdk-image.

After this PR

% make ensure-agones-sdk-image
/Library/Developer/CommandLineTools/usr/bin/make ensure-image IMAGE_TAG=gcr.io/agones-images/agones-sdk:1.24.0-8062a04-linux-amd64 BUILD_TARGET=build-agones-sdk-image
Could not find gcr.io/agones-images/agones-sdk:1.24.0-8062a04-linux-amd64 image. Building...
mkdir -p ~/.kube/
mkdir -p /Users/xxxxx/go/src/agones.dev/agones/build//.gocache
mkdir -p /Users/xxxxx/go/src/agones.dev/agones/build//.config/gcloud
mkdir -p ~/.config/helm
mkdir -p ~/.cache/helm
docker run --privileged --rm tonistiigi/binfmt:qemu-v6.2.0 --install arm64
...

Which issue(s) this PR fixes:

Closes #

Special notes for your reviewer:

[Ludea]

You save my day ! I'm on it since 2h -_-'

[agones-bot]

Build Failed 😱

Build Id: 309caa33-c7f2-4419-a680-3fd13ebed9db

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[Ludea]

lgtm
I apply this PR into #2591
And CI is green !

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

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

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [roberthbailey]

Approvers can indicate their approval by writing /approve in a comment
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[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

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

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [roberthbailey]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[agones-bot]

Build Succeeded 👏

Build Id: f7697487-c5bd-4b40-9c76-10cf09a5248a

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

• image: gcr.io/agones-images/agones-controller:1.24.0-7eef6ae-amd64
• image: gcr.io/agones-images/agones-controller:1.24.0-7eef6ae-arm64
• image: gcr.io/agones-images/agones-ping:1.24.0-7eef6ae
• Linux C++ SDK (build): agonessdk-1.24.0-7eef6ae-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.24.0-7eef6ae.zip

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

• https://7eef6ae-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2603/head:pr_2603 && git checkout pr_2603
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.24.0-7eef6ae-amd64