Ensure code generation dependencies are downloaded

[astefanutti]

What this PR does / why we need it:

This PR runs go mod download prior to running code generation to ensure the required dependencies are present.

Before:

$ sudo rm -rf `go list -m -mod=readonly -f "{{.Dir}}" k8s.io/code-generator`
$ make generate
GOBIN=/workdir/bin go install sigs.k8s.io/controller-tools/cmd/controller-gen@v0.16.5
/workdir/bin/controller-gen "crd:generateEmbeddedObjectMeta=true,maxDescLen=400" rbac:roleName=training-operator webhook paths="./pkg/apis/kubeflow.org/v1/..." \
    output:crd:artifacts:config=manifests/base/crds \
    output:rbac:artifacts:config=manifests/base/rbac \
    output:webhook:artifacts:config=manifests/base/webhook
/workdir/bin/controller-gen "crd:generateEmbeddedObjectMeta=true" rbac:roleName=training-operator-v2 webhook \
    paths="./pkg/apis/kubeflow.org/v2alpha1/...;./pkg/controller.v2/...;./pkg/runtime.v2/...;./pkg/webhook.v2/...;./pkg/cert/..." \
    output:crd:artifacts:config=manifests/v2/base/crds \
    output:rbac:artifacts:config=manifests/v2/base/rbac \
    output:webhook:artifacts:config=manifests/v2/base/webhook
/workdir/bin/controller-gen object:headerFile="hack/boilerplate/boilerplate.go.txt" paths="./pkg/apis/..."
hack/update-codegen.sh
hack/update-codegen.sh: line 19: /kube_codegen.sh: No such file or directory
make: *** [Makefile:52: generate] Error 1

After:

$ sudo rm -rf `go list -m -mod=readonly -f "{{.Dir}}" k8s.io/code-generator`
$ make generate
# OK

Checklist:

• [x] Docs included if any changes are user facing

[google-oss-prow[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Once this PR has been reviewed and has the lgtm label, please assign jeffwan for approval. For more information see the Kubernetes Code Review Process.

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

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[coveralls]

Pull Request Test Coverage Report for Build 12089250799

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 12088918617:	0.0%
Covered Lines:	77
Relevant Lines:	77

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💛 - Coveralls