Linting: need git ... --add safe.directory

[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
/kind release

What this PR does / Why we need it:

Ran into the ol' "error obtaining VCS status: exit status 128" issue, but this time with make lint.

Figured I'd move the command into a variable, so it can be reused across the Makefile.

Which issue(s) this PR fixes:

N/A

Special notes for your reviewer:

N/A

[agones-bot]

Build Succeeded 👏

Build Id: 20f0eea0-4f01-4866-8177-4752f262cb5d

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

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.39.0-dev-d40ce54-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.39.0-dev-d40ce54-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.39.0-dev-d40ce54-linux-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.39.0-dev-d40ce54-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.39.0-dev-d40ce54-amd64
• Linux C++ SDK (build): agonessdk-1.39.0-dev-d40ce54-amd64-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.39.0-dev-d40ce54-amd64.zip

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

• https://d40ce54-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/3638/head:pr_3638 && git checkout pr_3638
• helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.39.0-dev-d40ce54-amd64